Glossary of biotechnology for food and agriculture

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A - C

A Abbreviation for adenine.

Ab Abbreviation for antibody.

ABC model Widely accepted model of flower organ identity that appears generally applicable to distantly related dicotyledonous, although less well to monocotyledonous plants. The model incorporates the Arabidopsis genes required for flower organ identity.

abiotic Absence of living organisms.

abscisic acid A phytohormone implicated in the control of many plant responses to abiotic stress, such as extent of stomatal opening under water deficit (i.e. drought) conditions.

abzyme See: catalytic antibody.

acaricide A pesticide used to kill or control mites or ticks.

ACC synthase Abbreviation for 1-aminocyclopropane-1-carboxylase. The enzyme catalyses the rate limiting step in the ethylene biosynthetic pathway, and is particularly significant in the fruit ripening process. Plants typically carry a number of distinct ACC synthase genes, which are differentially regulated in response to a variety of developmental, environmental and chemical factors.

acceptor control The regulation of the rate of respiration by the availability of ADP as a phosphate acceptor.

acceptor junction site The junction between the 3' end of an intron and the 5' end of an exon. See: donor junction site.

accessory bud A lateral bud occurring at the base of a terminal bud or at the side of an axillary bud.

acclimatization The adaptation of a living organism (plant, animal or micro-organism) to a changed environment that subjects it to physiological stress. Acclimatization should not be confused with adaptation.

acellular Tissues or organisms that are not made up of separate cells but often have more than one nucleus.

acentric chromosome Chromosome fragment lacking a centromere.

acetyl CoA Abbreviation for acetyl co-enzyme A.

acetyl co-enzyme A (Abbreviation: acetyl CoA) A compound formed in the mitochondria when an acetyl group (CH₃CO-) - derived from breakdown of fats, proteins, or carbohydrates - combines with the thiol group (-SH) of co-enzyme A.

ACP Abbreviation for acyl carrier protein.

acquired Developed in response to the environment, not inherited, such as a character trait (acquired characteristic) resulting from environmental effect(s). cf acclimatization.

acridine dyes A class of positively charged polycyclic molecules that intercalate into DNA and induce frameshift mutations.

acrocentric A chromosome that has its centromere near the end.

acropetal Arising or developing in a longitudinal sequence beginning at the base and proceeding towards the apex. Opposite: basipetal.

activated carbon See activated charcoal.

activated charcoal Charcoal that has been treated to remove hydrocarbons and to increase its adsorptive properties. It acts by condensing and holding a gas or solute onto its surface; thus inhibitory substances in nutrient medium may be adsorbed to charcoal included in the medium.

active transport The movement of a molecule or groups of molecules across a cell membrane, which requires the expenditure of cellular energy, because the direction of movement is against the prevailing concentration gradient.

acute transfection Short-term transfection.

acyl carrier protein (Abbreviation: ACP). A class of molecules that bind acyl intermediates during the formation of long-chain fatty acids. ACPs are important because of their involvement in many of the reactions necessary for in vivo fatty acid synthesis.

adaptation Adjustment of a population to changes in environment over generations, associated (at least in part) with genetic changes resulting from selection imposed by the changed environment. Not acclimatization.

additive genes Genes whose net effect is the sum of their individual allelic effects, i.e. they show neither dominance nor epistasis.

additive genetic variance The net effect of the expresson of additive genes, and thus the chief cause of the resemblance between relatives. It represents the main determinant of the response of a population to selection. Formally, the variance of breeding values.

adenine (Abbreviation: A). One the bases found in DNA and RNA. See: adenosine.

adenosine The (ribo)nucleoside resulting from the combination of the base adenine (A) and the sugar D-ribose. The corresponding deoxyribonucleoside is called deoxyadenosine. See: adenosine triphosphate, adenylic acid, dATP.

adenosine diphosphate (adenosine 5'-diphosphate) (Abbreviation: ADP). See: adenosine triphosphate.

adenosine monophosphate (adenosine 5'-monophosphate) (Abbreviation: AMP). See: adenylic acid, adenosine triphosphate.

adenosine triphosphate (adenosine 5'-triphosphate) (Abbreviation: ATP). A nucleotide of fundamental importance as the major carrier of chemical energy in all living organisms. It is also required for RNA synthesis since it is a direct precursor molecule. ATP consists of adenosine with three phosphate groups, linked together linearly. The phosphates are attached to adenosine through the 5'-hydroxyl of its ribose (sugar) portion. Upon hydrolysis, these bonds yield either one molecule of adenosine 5'-diphosphate (ADP) and the inorganic phosphate ion, or one molecule of adenosine 5'-monophosphate (AMP) and pyrophosphate; in both cases releasing energy that is used to power biological processes. ATP is regenerated by the phosphorylation of AMP and ADP.

adenovirus One of a group of DNA-containing viruses found in rodents, fowl, cattle, monkeys, and man. In man they are responsible for respiratory-tract infections, but they have been exploited as a vector in gene therapy, especially for genes targeted at the lungs.

adenylic acid Synonym for adenosine monophosphate, a (ribo)nucleotide containing the nucleoside adenosine. The corresponding deoxyribonucleotide is called deoxyadenosine 5'-monophosphate or deoxyadenylic acid.

adoptive immunization The transfer of an immune state from one animal to another by means of lymphocyte transfusions.

ADP Abbreviation for adenosine diphosphate.

adventitious A structure arising at sites other than the usual ones, e.g. shoots from roots or leaves, and embryos from any cell other than a zygote.

aerobe A micro-organism that grows in the presence of oxygen. Opposite: anaerobe.

aerobic Active in the presence of free oxygen, e.g. aerobic bacteria that can live in the presence of oxygen.

aerobic respiration A type of respiration in which foodstuffs are completely oxidized to carbon dioxide and water, with the release of chemical energy, in a process requiring atmospheric oxygen.

affinity chromatography A method for purifying specific components in a solution by exploiting their specific binding to known molecule(s). The mixed solution is passed through a column containing a solid medium to which the binding molecule is covalently attached. See: immunoaffinity chromatography; metal affinity chromatography; pseudo-affinity chromatography.

affinity tag An amino acid sequence that has been engineered into a protein to make its purification easier. The tag could be another protein or a short amino acid sequence, allowing purification by affinity chromatography. Synonym: purification tag.

aflatoxins A group of toxic compounds, produced by Aspergillus flavus, that bind to DNA and prevent replication and transcription. Aflatoxins can cause acute liver damage and cancer. A health hazard in certain stored foods or feed.

AFLP Abbreviation for amplified fragment length polymorphism.

Ag Abbreviation for antigen.

agar A polysaccharide gelifying agent used in nutrient media preparations and obtained from Rhodophyta (red algae). Both the type of agar and its concentration can affect the growth and appearance of cultured explants.

agarose The main functional constituent of agar.

agarose gel electrophoresis A method to separate DNA and RNA molecules on the basis of their size, in which samples are subjected to an electric field applied to a gel made with agarose.

aggregate 1. A clump or mass formed by gathering or collecting units. 2. A body of loosely associated cells, such as a friable callus or cell suspension. 3. Coarse inert material, such as gravel, that is mixed with soil to increase its porosity. 4. A serological reaction in which the antibody and antigen react and precipitate.

agonist A drug, hormone or transmitter substance that forms a complex with a receptor site. The formation of the complex triggers an active response from a cell.

Agrobacterium A genus of bacteria that includes several plant pathogenic species, causing tumour-like symptoms. See: Agrobacterium rhizogenes, Agrobacterium tumefaciens.

Agrobacterium rhizogenes A bacterium that causes hairy root disease in some plants. Similar to the crown gall disease caused by Agrobacterium tumefaciens, this is achieved by the mobilization of the bacterial Ri plasmid with the transfer to the plant of some of the genetic material from the plasmid. This process has been used to insert foreign genes into plant cells, but to a lesser extent than the Agrobacterium tumefaciens-mediated transformation system, because regeneration of whole plants from hairy root cultures is problematical.

Agrobacterium tumefaciens A bacterium that causes crown gall disease in some plants. The bacterium characteristically infects a wound, and incorporates a segment of Ti plasmid DNA into the host genome. This DNA causes the host cell to grow into a tumour-like structure that synthesizes specific opines that only the pathogen can metabolize. This DNA-transfer mechanism is exploited in the genetic engineering of plants. See: T-DNA.

Agrobacterium tumefaciens-mediated transformation The process of DNA transfer from Agrobacterium tumefaciens to plants, that occurs naturally during crown gall disease, and can be used as a method of transformation.

AHG Abbreviation for antihaemophilic globulin.

AI Abbreviation for artificial insemination.

airlift fermenter A cylindrical fermentation vessel in which the cells are mixed by air introduced at the base of the vessel and that rises through the column of culture medium. The cell suspension circulates around the column as a consequence of the gradient of air bubbles in different parts of the reactor.

albinism Hereditary absence of pigment in an organism. Albino animals have no colour in their skin, hair and eyes. Albino plants lack chlorophyll.

albino 1. An organism lacking pigmentation, due to genetic factors. The condition is albinism 2. A conspicuous plastid mutant involving loss of chlorophyll.

aleurone The outermost layer of the endosperm in a seed, and the site of enzymes concerned with endosperm digestion during seedling growth.

algal biomass Single-celled plants (e.g. Chlorella spp. and Spirulina spp.) grown commercially in ponds to make feed materials for zooplankton, which are in turn harvested as feed for fish farms.

alginate Polysaccharide gelling agent.

alkylating agent A class of chemicals that transfer alkyl (methyl, ethyl, etc.) groups; for example to the bases in DNA. Some of these (especially ethyl methane sulphonate, abbreviated EMS) have been much used as mutagens.

allele A variant form of a gene. In a diploid cell there are two alleles of every gene (one inherited from each parent, although they could be identical). Within a population there may be many alleles of a gene. Alleles are symbolized with a capital letter to denote dominance, and lower case for recessive. In heterozygotes with co-dominant alleles, both are expressed. See: multiple alleles. Synonym: allelomorph.

allele frequency The relative number of copies of an allele in a population, expressed as a proportion of the total number of copies of all alleles at a given locus in a population.

allelic (adj.) See allele.

allele-specific amplification (Abbreviation: ASA). The use of the polymerase chain reaction at a sufficiently high stringency that only one allele is amplified. A powerful means of genotyping for single-locus disorders that have been characterized at the molecular level.

allelic exclusion A phenomenon whereby only one functional allele of an antibody gene can be assembled in a given B lymphocyte.

allelomorph See: allele.

allelopathy The secretion of chemicals, such as phenolic and terpenoid compounds, by a plant's roots, which inhibit the growth or reproduction of competitor plants.

allergen An antigen that provokes an immune response.

allogamy Cross fertilization in plants. See: fertilization.

allogenic Differing at one or more loci, although belonging to the same species. Thus an organ transplant from one human donor to another is allogeneic, whereas a transplant from a baboon to a human would be xenogeneic.

allometric When the growth rate of one part of an organism differs from that of another part or of the rest of the body.

allopatric In the context of natural populations of animals or plants, inhabiting distinct and separate areas.

allopatric speciation Speciation occurring at least in part because of geographic isolation.

allopolyploid A polyploid organism with sets of chromosomes derived from different species. Opposite: autopolyploid.

allosome Synonym for sex chromosome.

allosteric control See: allosteric regulation.

allosteric enzyme An enzyme that has two structurally distinct forms, one of which is active and the other inactive. Active forms tend to catalyse the initial step in a pathway leading to the synthesis of molecules. The end product of this synthesis can act as a feedback inhibitor, converting the enzyme to the inactive form, thus controlling the amount of product synthesized. Synonym: allozyme.

allosteric regulation A catalysis-regulating process in which the binding of a small effector molecule to one site on an enzyme affects the activity at another site.

allosteric site That part of an enzyme molecule where the non-covalent binding of an effector molecule can affect the enzyme's catalytic activity. See: conformation, ligand.

allosteric transition A reversible interaction of a small molecule with a protein molecule, resulting in a change in the shape of the protein and consequent alteration of the interaction of that protein with a third molecule.

allotetraploid An allopolyploid having two different progenitor genomes.

allotype A classification of antibody molecules according to the antigenicity of the constant regions; a variation that is determined by a single allele.

allozygote A individual that is heterozygous for two different mutant alleles.

allozyme See: allosteric enzyme.

alpha globulin See: haptoglobin.

alternative mRNA splicing The inclusion or exclusion of different exons to form different mRNA transcripts from a single transcription unit.

Alu sequences A highly repeated family of 300-bp long sequences dispersed throughout the human genome, so named because they are released by the digestion of genomic DNA with the restriction endonuclease AluI.

amber stop codon See: stop codon.

amino acid A compound containing both amino (-NH₂) and carboxyl (-COOH) groups. In particular, any of 20 basic building blocks of proteins having the formula NH₂-CR-COOH, where R is different for each specific amino acid. See: annex 3.

aminoacyl site (Abbreviation: A-site). One of two sites on ribosomes to which the aminoacyl tRNA molecules can bind.

aminoacyl tRNA synthetase An enzyme that catalyses the attachment of an amino acid to its specific tRNA molecule.

amitosis A cell division (including nuclear division through constriction of the nucleus) that occurs without chromosome differentiation as in mitosis. The mechanism whereby the genetic integrity is maintained during amitosis is uncertain.

amniocentesis A procedure for obtaining foetal cells for prenatal diagnosis by sampling the amniotic fluid from a pregnant mammal. Cells are cultured, and the karyotype is checked for known irregularities (e.g. Down's syndrome and spina bifida in humans).

amnion The thin membrane that lines the fluid-filled sac in which the embryo develops in higher vertebrates, reptiles and birds.

amniotic fluid Liquid contents of the amniotic sac of higher vertebrates, containing foetal, but not maternal cells.

amorph A mutation that abolishes gene function. Synonym: null mutation.

AMP Abbreviation for adenosine monophosphate.

amphidiploid A plant derived from doubling the chromosome number of an interspecific F₁ hybrid. Naturally found hybrids of this sort are referred to as allopolyploid.

amphimixis True sexual reproduction involving the fusion of male and female gametes and the formation of a zygote.

ampicillin A penicillin-type antibiotic that prevents bacterial growth by interfering with synthesis of the cell wall. Commonly used as a selectable marker in the creation of transgenic plants.

amplicon The product of a DNA amplification reaction. See: polymerase chain reaction.

amplification 1. Creation of many copies of a segment of DNA by the polymerase chain reaction. 2. Treatment (e.g. use of chloramphenicol) designed to increase the proportion of plasmid DNA relative to that of bacterial (host) DNA. 3. Evolutionary expansion in copy number of a repetitive DNA sequence through a process of repeated duplication.

amplified fragment length polymorphism (Abbreviation: AFLP). A type of DNA marker, generated by the PCR amplification of restriction endonuclease treated DNA. A small proportion of all restriction fragments is amplified in any one reaction, so that AFLP profiles can be analysed by gel electrophoresis. This has the important characteristic that many markers can be generated with relatively little effort.

amplify To increase the number of copies of a DNA sequence, either in vivo by inserting into a cloning vector that replicates within a host cell, or in vitro by polymerase chain reaction.

ampometric See: electrochemical sensor

amylase Describing a wide class of enzymes that catalyse the hydrolysis of starch.

amylolytic The capability of enzymatically degrading starch into sugars.

amylopectin A polysaccharide comprising highly branched chains of glucose residues. The water-insoluble portion of starch.

amylose A polysaccharide consisting of linear chains of 100-1000 glucose residues. The water-soluble portion of starch.

anabolic pathway A pathway by which a metabolite is synthesized; a biosynthetic pathway.

anabolism One of the two subcategories of metabolism, referring to the building up of complex organic molecules from simpler precursors.

anaerobe An organism that can grow in the absence of oxygen. Opposite: aerobe.

anaerobic An environment or condition in which molecular oxygen is not available for chemical, physical or biological processes.

anaerobic digestion Digestion of materials in the absence of oxygen. See: anaerobic respiration.

anaerobic respiration Respiration in which foodstuffs are partially oxidized, with the release of chemical energy, in a process not involving atmospheric oxygen. A notable example is in alcoholic fermentation, where sugar is metabolized into ethanol.

analogous Features of organisms or molecules that are superficially or functionally similar but have evolved in a different way or contain different compounds.

anaphase The stage of mitosis or meiosis during which the daughter chromosomes migrate to opposite poles of the cell (toward the ends of the spindle). Anaphase follows metaphase and precedes telophase.

anchor gene A gene that has been positioned on both the physical map and the linkage map of a chromosome, and thereby allows their mutual alignment.

androgen Any hormone that stimulates the development of male secondary sexual characteristics, and contributes to the control of sexual activity in vertebrate animals. Usually synthesized in the testis.

androgenesis Male parthenogenesis, i.e. the development of a haploid embryo from a male nucleus. The maternal nucleus is eliminated or inactivated subsequent to fertilization of the ovum, and the haploid individual (referred to as androgenetic) contains in its cells the genome of the male gamete only. See: anther culture; gynogenesis.

aneuploid An organism or cell having a chromosome number other than the normal somatic number. Aneuploid gametes have a chromosome number other than the normal haploid number. The condition is aneuploidy.

angiogenesis The formation and development of new blood vessels in the body, stimulated by growth factors, such as angiogenin. The process is required for the spread of malignant tumours.

angiogenin One of the human angiogenic growth factors. In addition to stimulating (normal) blood vessel formation, angiogenin levels are correlated with placenta formation and tumour growth.

angiosperm A division of the plant kingdom that includes all flowering plants, i.e. vascular plants in which double fertilization occurs resulting in development of fruit containing seeds. Divided into two major groups, monocotyledons and dicotyledons. See: gymnosperm

animal cell immobilization Entrapment of animal cells in some solid material in order to produce some natural product or genetically engineered protein. Animal cells have the advantage that they already produce many proteins of pharmacological interest, and that genetically engineered proteins are produced by them with the post-translation modifications normal to animals. However, because animal cells are much more fragile than bacterial ones, they cannot tolerate a commercial fermentation process.

animal cloning See: cloning.

anneal The pairing of complementary DNA or RNA sequences, via hydrogen bonding, to form a double-stranded polynucleotide. Opposite: denature.

annual 1. (adj:) Taking one year, or occurring at intervals of one year. 2. A plant that completes its life cycle within one year. See biennial, perennial.

anonymous DNA marker A DNA marker detectable by virtue of variation in its sequence. The function (if any) of the sequence is unknown. Microsatellites and AFLPs are typical anonymous DNA markers.

antagonism An interaction between two organisms (e.g. moulds or bacteria) in which the growth of one is inhibited by the other. Opposite: synergism.

antagonist A compound that inhibits the effect of an agonist in such a way that the combined biological effect of the two becomes smaller than the sum of their individual effects.

anther The upper part of a stamen, containing pollen sacs within which the pollen develops and matures.

anther culture The aseptic culture of immature anthers to generate haploid plants from microspores via androgenesis.

anthesis The period during which anthers bear mature and functional pollen.

anthocyanin A water-soluble blue, purple or red flavonoid pigments found in vacuoles of cells of certain plants.

antiauxin A chemical that interferes with the auxin response, sometimes by the prevention of auxin transport. Some antiauxins may promote morphogenesis in vitro (e.g. 2,3,5-tri-iodobenzoate (TIBA) and 2,4,5-trichlorophenoxyacetate (2,4,5-T)) and are therefore used to stimulate the growth of some cultures.

antibiosis The prevention of growth or development of an organism by a substance or another organism.

antibiotic A class of natural and synthetic compounds that inhibit the growth of, or kill some micro-organisms. Antibiotics are widely used medicinally to control bacterial pathogens, but resistance in bacteria to particular antibiotics is often rapidly acquired through mutation.

antibiotic resistance The ability of a micro-organism to disable an antibiotic or prevent its transport into the cell.

antibiotic resistance marker gene (Abbreviation: ARMG). Genes (usually of bacterial origin) used as selection markers in transgenesis, because their presence allows cell survival in the presence of normally toxic antibiotic agents. These genes were commonly used in the development and release of first generation transgenic organisms (particularly crop plants), but are no longer favoured because of perceived risks associated with the unintentional transfer of antibiotic resistance to other organisms. See kan^r, neo^r.

antibody (Abbreviation: Ab). An immunological protein produced by the lymphocytes in response to contact with an antigen. Each antibody recognizes just one antigenic determinant of one antigen and acts by specifically binding to it, thus rendering it harmless. Those from the IgG antibody class are found in the bloodstream and used in immunoassay. Synonym: immunoglobulin. See: monoclonal antibody, polyclonal antibody.

antibody binding site The part of an antibody that binds to the antigenic determinant. See: complementarity-determining regions. Synonym: paratope.

antibody class The class to which an antibody belongs, depending on the type of heavy chain present. In mammals, there are five classes of antibodies: IgA, IgD, IgE, IgG, and IgM.

antibody structure Describes the molecular architecture of an antibody, which consists of two identical "light" chains and two identical "heavy" chains and has two antigen-binding sites. Each chain consists of a constant region which is the same between antibodies of the same class and sub-class, and a variable region that is antibody-specific.

antibody-mediated immune response The synthesis of antibodies by B cells in response to an encounter of the cells of the immune system with a foreign antigen. Synonym: humoral immune response.

anticlinal The orientation of cell wall or plane of cell division perpendicular to the surface. Opposite: periclinal.

anticoding strand The DNA strand used as template for transcription. The resulting mRNA is complementary in sequence to that of the anticoding strand. Synonym: template strand.

anticodon A triplet of tRNA nucleotides that corresponds to a complementary codon in an mRNA molecule during translation.

antigen (Abbreviation: Ag). A macromolecule (usually a protein foreign to the organism), which elicits an immune response on first exposure to the immune system by stimulating the production of antibodies specific to its various antigenic determinants. During subsequent exposures, the antigen is bound and inactivated by these antibodies. Synonym: immunogen.

antigenic determinant The individual surface feature of an antigen, that elicits the production of a specific antibody in the course of the immune response. Each antigenic determinant, typically a few amino acids in size, causes the synthesis of a different antibody and thus exposure to a single antigen may result in the expression of a number of antibodies. See: monoclonal antibody, polyclonal antibody. Synonym: epitope.

antigenic switching The altering of a micro-organism's surface antigens through genetic re-arrangement, to elude detection by the host's immune system.

antihaemophilic factor VIII See: antihaemophilic globulin.

antihaemophilic globulin (Abbreviation AHG). One of the blood clotting factors, a soluble protein that causes the fibrin matrix of a blood clot to form. Used as a treatment for haemophilia, AHG is usually obtained from genetically engineered cell cultures. Synonym: antihaemophilic factor VIII.

anti-idiotype antibody An antibody, produced by an organism, which specifically binds to the binding site of an antibody developed by that organism against a foreign antigen. Involved with the regulation of the immune response. Some allergic responses are in part due to the breakdown of this sort of regulation.

antimicrobial agent Any chemical or biological agent that inhibits the growth and/or survival of micro-organisms. See: antibiotic.

antinutrient Compounds that inhibit the normal uptake or utilization of nutrients.

anti-oncogene A gene whose product prevents the normal growth of tissue.

antioxidant Compounds that slow the rate of oxidation reactions.

antiparallel orientation The normal arrangement of the two strands of a double-stranded DNA molecule, and of other nucleic-acid duplexes (DNA-RNA, RNA-RNA), in which the two strands are oriented in opposite directions so that the 5'-phosphate end of one strand is aligned with the 3'-hydroxyl end of the complementary strand.

antisense DNA One of the two strands of double-stranded DNA, usually that which is complementary (hence "anti") to the mRNA, i.e. the non-transcribed strand. However, there is not universal agreement on this convention, and the preferred designations are coding strand for the strand whose sequence matches that of the mRNA, and non-coding strand or template strand for the complementary strand (i.e. the transcription template).

antisense gene A gene that produces an mRNA complementary to the transcript of a normal gene (usually constructed by inverting the coding region relative to the promoter).

antisense RNA An RNA sequence that is complementary to all or part of a functional mRNA molecule, to which it binds, blocking its translation.

antisense therapy The in vivo treatment of a genetic disease by blocking translation of a protein with a DNA or an RNA sequence that is complementary to a specific mRNA.

antiseptic Any substance that kills or inhibits the growth of disease-causing micro-organism (a micro-organism capable of causing sepsis), but is essentially non-toxic to cells of the body.

antiserum The fluid portion of the blood of an immunized animal (after coagulation of the blood), which retains any antibodies.

anti-terminator A protein which enables RNA polymerase to ignore certain transcriptional stop or termination signals and thereby produce longer than normal transcripts.

antitranspirant A compound designed to reduce plant transpiration. Applied to the leaves of newly transplanted trees, shrubs etc., or cuttings in lieu of misting. Can interfere with photosynthesis and respiration if the coating is too thick or is unbroken.

antixenosis The modification of the behaviour of an organism by a substance or another organism. Particularly used in the context of a plant's apparent resistance against insect feeding, when the insects are presented with a choice of plant genotypes.

apex The portion of a root or shoot containing the primary or apical meristem.

apical cell A meristematic initial in the apical meristem of shoots or roots of plants.

apical dominance The phenomenon where growth of lateral (axillary) buds in a plant is inhibited by the presence of the terminal (apical) bud on the branch. Explained by the export of auxins from the apical bud.

apical meristem A region of the tip of each shoot and root of a plant in which cell division is continually occurring to produce new stem and root tissue, respectively. Two regions are visible in the apical meristem: An outer 1-4-cell layered region (the tunica), where cell divisions are anticlinal; and below the tunica, (ii) the corpus, where the cells divide in all directions, and increase in volume.

apoenzyme Inactive enzyme that has to be associated with a co-enzyme in order to function. The apoenzyme/co-enzyme complex is called a holoenzyme.

apomixis The production of an embryo in the absence of meiosis. Apomictic higher plants produce asexual seeds, derived only from maternal tissue. See: parthenogenesis.

apoptosis The process of programmed cell death, which occurs naturally as a part of normal development, maintenance and renewal of tissue. Differs from necrosis, in which cell death is caused by external factors (stress or toxin).

AP-PCR See: arbitrarily primed polymerase chain reaction.

aptamer A polynucleotide molecule that binds to a specific molecule, often a protein.

aquaculture Farming of aquatic organisms, including fish, molluscs, crustaceans and aquatic plants.

Arabidopsis A genus of flowering plants in the Cruciferae. A. thaliana is used in research as a model plant because it has a small fully sequenced genome, can be cultured and transformed easily, and has a rapid generation time.

arbitrarily primed polymerase chain reaction (Abbreviation: AP-PCR) An application of the polymerase chain reaction to generate DNA fingerprints. The technique uses arbitrary primers to amplify anonymous stretches of DNA. See: DNA amplification fingerprinting, random amplified polymorphic DNA.

arbitrary primer An oligonucleotide primer whose sequence is chosen at random, rather than one whose sequence matches that of a known locus. These primers therefore amplify DNA fragments which have not been pre-selected.

Archaea Single-celled life forms adapted to existence in high pressure, anaerobic, environments such as at extreme ocean depths. These organisms are seen as a promising source of enzymes robust enough for a number of demanding industrial processes.

ARMG Abbreviation for antibiotic resistance marker gene.

ARS Abbreviation for autonomous(ly) replicating segment (or sequence).

artificial inembryonation Non-surgical transfer of embryo(s) to a recipient female. As in vitro embryo technology develops, artificial inembryonation may replace artificial insemination.

artificial insemination (Abbreviation: AI). The deposition of semen, using a syringe, at the mouth of the uterus to make conception possible.

artificial medium See: culture medium.

artificial seed Encapsulated or coated somatic embryos that are planted and treated like seed.

artificial selection The practice of choosing individuals from a population for reproduction, usually because these individuals possess one or more desirable traits.

ASA Abbreviation for allele-specific amplification.

ascites Abnormal accumulation of fluid in the peritoneal cavity, occurring naturally as a complication of cirrhosis of the liver, among other conditions. In the context of monoclonal antibody production, hybridoma cells are injected into mice to induce their proliferation in the resulting ascites. This method has been largely superseded by in vitro culture of hybridomas.

ascospore One of the spores contained in the ascus of certain fungi.

ascus (pl.: asci) Reproductive sac in the sexual stage of a type of fungi (Ascomycetes) in which ascospores are produced.

aseptic Sterile, free of contaminating organisms (bacteria, fungi, algae but not generally including viruses, and particularly not internal symbionts).

asexual Reproduction not involving meiosis or the union of gametes.

asexual embryogenesis See: somatic cell embryogenesis.

asexual propagation Vegetative, somatic, non-sexual reproduction of a plant without fertilization.

asexual reproduction Reproduction that does not involve the formation and union of gametes from the different sexes or mating types. It occurs mainly in lower animals, micro-organisms and plants. In plants, asexual reproduction is by vegetative propagation (e.g. bulbs, tubers, corms) and by formation of spores.

A-site Abbreviation for aminoacyl site.

assay 1. To test or evaluate. 2. The procedure for measuring the quantity of a given substance in a sample (chemically or by other means).

assortative mating Mating in which the partners are chosen on the basis of phenotypic similarity.

assortment See: segregation.

asymmetric hybrid A hybrid formed, usually via protoplast fusion, between two donors, where the chromosome complement of one of the donors is incomplete. This chromosome loss can be induced by irradiation or chemical treatment, or can occur naturally.

asynapsis The failure or partial failure in the pairing of homologous chromosomes during the first meiotic prophase.

ATP Abbreviation for adenosine triphosphate.

ATP-ase An enzyme that brings about the hydrolysis of adenosine triphosphate, by the cleavage of either one phosphate groups with the formation of ADP and inorganic phosphate, or of two phosphate groups, with the formation of AMP and pyrophosphate.

attenuated vaccine A virulent organism that has been modified to produce a less virulent form, but nevertheless retains the ability to elicit antibodies against the virulent form. See: inactivated agent.

attenuation A mechanism for controlling gene expression in prokaryotes that involves premature termination of transcription.

attenuator A nucleotide sequence in the 5' region of a prokaryotic gene (or in its RNA) that causes premature termination of transcription, possibly by forming a secondary structure.

aureofacin An antifungal antibiotic produced by a strain of Streptomyces aureofaciens. A possible candidate for the transgenic control of plant fungal disease.

authentic protein A recombinant protein that has all the properties - including any post-translational modifications - of its naturally occurring counterpart.

autocatalysis Catalysis in which one of the products of the reaction is a catalyst for the reaction.

autocatalytic reaction See: autocatalysis.

autoclave 1. An enclosed chamber in which materials can be heated under pressure to sterilize utensils, liquids, glassware, etc., using steam.

autogenous control The action of a gene product to inhibit (negative autogenous control) or enhance (positive autogenous control) the expression of the gene that codes for it.

auto-immune disease Disorder in which the immune systems of affected individuals produce antibodies against molecules that are normally produced by those individuals (called self antigens).

auto-immunity A disorder in the body's defence mechanism in which an immune response is elicited against its own (self) tissues.

autologous cells Cells taken from an individual, cultured (or stored), and, possibly, genetically manipulated before being transferred back into the original donor.

autolysis The process of self destruction of a cell, cell organelle, or tissue, through the action of lysosomic enzymes.

autonomous A term applied to any biological unit that can function on its own, i.e. without the help of another unit, such as a transposable element that encodes an enzyme for its own transposition.

autonomous(ly) replicating segment (or sequence) (Abbreviation: ARS). Any eukaryotic DNA sequence that initiates and supports chromosomal replication; they have been isolated in yeast cells.

autopolyploid A polyploid whose constituent genomes are derived from the same or nearly the same progenitor. In an autotetraploid, each chromosome is present in four copies, so meiotic configurations may include many (or exclusively) quadrivalents (four paired chromosomes), and the inheritance of alleles will be quadruplex. Quadrivalents do not always segregate normaly at meiosis, resulting in lowered fertility, so some established autotetraploid species that reproduce sexually have restricted quadrivalent formation.

autoradiograph A technique for visualizing the presence, location and intensity of radioactivity in histological preparations, paper chromatograms or electrophoretic gel separations, obtained by overlaying the surface with X-ray film and allowing the radiation to form an image on the film.

autosome Any of the chromosomes except the sex chromosomes.

autotroph Organism capable of self-nourishment utilizing carbon dioxide or carbonates as the sole source of carbon and obtaining energy from radiant energy or from the oxidation of inorganic elements, or compounds such as iron, sulphur, hydrogen, ammonium and nitrites. Opposite: heterotroph.

autotrophic (adj.) See: autotroph.

auxin A group of plant growth regulators (natural or synthetic) which stimulate cell division, enlargement, apical dominance, root initiation, and flowering.

auxin-cytokinin ratio The relative proportion of auxin to cytokinin present in plant tissue culture media. Varying the relative amounts of these two hormones affects the proportional growth of shoots and roots.

auxotroph A mutant cell or micro-organism lacking one metabolic pathway present in the parental strain, and that consequently will not multiply on a minimal medium, but requires for growth the addition of a specific compound, such as an amino acid or a vitamin.

availability A reflection of the form and location of nutritional elements and their suitability for absorption.

avidin A glycoprotein present in egg white, which has a strong affinity to biotin. Can lead to biotin deficiency if given in large quantities. Used as a biological reagent in the same way as streptavidin.

avidity A measure of the binding strength of an antibody to its antigen.

avirulence gene (Abbreviation: avr gene). Many plants contain R genes, which confer simply-inherited resistance to a specific pathogen race. The plants are able to recognize the presence of the pathogen by an interaction between their R gene and the matching pathogen's avirulence gene. Successful recognition triggers a cascade of further genes, often leading to a hypersensitive response.

avr gene Abbreviation for avirulence gene.

axenic culture Free of external contaminants and internal symbionts; generally not possible with surface sterilization alone, sometimes used incorrectly to indicate aseptic culture.

axillary bud A bud found at the axil of a leaf. Synonym: lateral bud.

axillary bud proliferation Propagation of plant tissue in vitro to promote axillary growth, to generate large numbers of plantlets in culture.

B cell An important class of lymphocytes that mature in bone marrow (in mammals) and the Bursa of Fabricius (in birds) and produce antibodies. Largely responsible for the antibody-mediated or humoral immune response, giving rise to the antibody-producing plasma cells and some other cells of the immune system. Synonym: B lymphocyte.

B chromosome A supernumerary chromosome present in some individuals (both plant and animal). They are smaller than the normal chromosomes, behave abnormally in both mitosis and meiosis, can vary in number between somatic cells and are not thought to have any significant gene content.

B lymphocyte See: B cell.

BABS Abbreviation for biosynthetic antibody binding sites.

BAC Abbreviation for bacterial artificial chromosome.

bacillus A rod-shaped bacterium.

Bacillus thuringiensis (Abbreviation: Bt). A bacterium that produces a toxin against certain insects, particularly Coloeoptera and Lepidoptera; a major means of insecticide for organic farming. Some of the toxin genes are important for transgenic approaches to crop protection.

back mutation A second mutation at the same site in a gene as the original mutation. The second mutation restores the wild-type protein sequence.

backcross Crossing an individual with one of its parents or with the genetically equivalent organism. The offspring of such a cross are referred to as the backcross generation or backcross progeny.

bacterial artificial chromosome A plasmid vector that can be used to clone large inserts of DNA (up to 500 kb). See: yeast artificial chromosome.

bacterial toxin A toxin produced by a bacterium, such as Bt toxin of Bacillus thuringiensis.

bacteriocide A chemical or drug that kills bacterial cells.

bacteriocin A protein produced by bacteria of one strain and active against those of a closely related strain.

bacteriophage (Abbreviation: phage). A virus that infects bacteria. Altered forms are used as cloning vectors. See: lambda phage, M13.

bacteriostat A substance that inhibits or slows down growth and reproduction of bacteria.

bacterium (pl.: bacteria) nicellular prokaryotic organisms, without a distinct nucleus. Major distinctive groups are defined by Gram staining. Also classified on the basis of oxygen requirement (aerobic vs anaerobic) and shape (spherical = coccus; rodlike = bacillus; spiral = spirillum; comma-shaped = vibrio; corkscrew-shaped = spirochaete; filamentous).

baculovirus A class of insect virus used to make DNA cloning vectors for gene expression in eukaryotic cells. Production of a target protein can be up to 50% of the cells' protein content, and several proteins can be made simultaneously, so that multi-sub-unit enzymes can be made by this system.

baculovirus expression vector (Abbreviation: BEV). A method for the in vitro production of complex recombinant eukaryotic proteins. A genetically engineered baculovirus (a virus that infects certain types of insects) is introduced into appropriate cultured insect cells, which then express the recombinant protein.

balanced lethal system A system for maintaining a recessive lethal allele at each of two loci on the same pair of chromosomes. In a closed population with no crossing-over between the loci, only the double heterozygotes for the lethal mutations survive.

balanced polymorphism Two or more phenotypes maintained in the same breeding population.

bank See: gene bank.

bar gene See: pat gene.

barnase A bacterial ribonuclease, which, when transformed into plants and expressed in the anthers, generates a male sterile phenotype. Thus it is a technology applicable to F₁ hybrid seed production, which relies on the ability to genetically sterilize genotypes to ensure that all seed borne on the plant are the result of outcrossing. The sterility phenotype is suppressed by the barstar protein, which can therefore be used to reverse the sterility where this is necessary.

Barr body A condensed mass of chromatin found in the nuclei of female mammals. It is a late-replicating, inactive X-chromosome. See: dosage compensation, sex linkage

barstar protein A polypeptide inhibitor of barnase.

basal 1. Located at the base of a plant or a plant organ. 2. A fundamental formulation of a tissue culture medium containing nutrients but no growth promoting agents.

base One of the components of nucleosides, nucleotides and nucleic acids. Four different bases are found in naturally occurring DNA - the purines A (adenine) and G (guanine); and the pyrimidines C (cytosine) and T (thymine, the common name for 5-methyluracil). In RNA, T is replaced by U (uracil). See: base pair.

base analogue A non-natural purine or pyrimidine base that differs slightly in structure from the normal bases, but can be incorporated into nucleic acids. They are often mutagenic.

base pair (Abbreviation: bp). The two separate strands of a nucleic acid double helix are held together by specific hydrogen bonding between a purine and a pyrimidine, one from each strand. The base A pairs with T in DNA (with U in RNA); while G pairs with C in both DNA and RNA. The length of a nucleic acid molecule is often given in terms of the number of base pairs it contains.

base substitution Replacement of one base by another in a DNA molecule. See: transition; transversion.

basic fibroblast growth factor (Abbreviation: BFGF). See: fibroblasts.

basipetal Developing, in sequence, from the apex towards the base. See: acropetal.

basophil A type of leukocyte produced by stem cells in the red bone marrow.

batch culture A suspension culture in which cells grow in a finite volume of liquid nutrient medium and follow a sigmoid pattern of growth. All cells are harvested at the same time. See: continuous culture. Synonym: batch fermentation.

batch fermentation See: batch culture.

bench-scale process A small- or laboratory-scale process; commonly used in connection with fermentation.

beta-DNA The form of DNA generally found in nature. A right-handed helix.

beta-galactosidase A bacterial enzyme that catalyses the cleavage of lactose into glucose and galactose, commonly used as a marker in DNA cloning.

beta-glucuronidase (Abbreviation: GUS). An enzyme produced by certain bacteria, which catalyses the cleavage of a whole range of beta-glucuronides. Because this activity is largely absent in plants, the encoding bacterial gene has been widely used as a reporter gene in plant transgenesis.

beta-lactamase An enzyme that detoxifies penicillin group antibiotics, such as ampicillin. The â-lactamase gene is commonly used as a marker for successful transformation, where only transformed cells are able to tolerate the presence of ampicillin. See: selectable marker.

beta-sitosterol See: phytosterol.

BEV Abbreviation for baculovirus expression vector.

BFGF Abbreviation for basic fibroblast growth factor.

biennial A plant which completes its life cycle within two years and then dies.

bifunctional vector See: shuttle vector.

binary vector system A two plasmid system in Agrobacterium tumefaciens designed to transfer T-DNA into plant cells, while avoiding the formation of crown gall tumours. One plasmid contains the virulence gene (responsible for transfer of the T-DNA), and the other the T-DNA borders, the selectable marker and the DNA to be transferred.

binding The ability of molecules to bind each other non-covalently because of the exact shape and chemical nature of parts of their surfaces. A common biological phenomenon, as e.g. an enzyme to its substrate; an antibody to its antigen; a DNA strand to its complementary strand. See: ligand.

bio- A prefix used in scientific words to associate the concept of "living organisms." Usually written with a hyphen before vowels, for emphasis or in neologisms.

bio-accumulation A problem that can arise when a stable chemical such as a heavy metal or DDT is introduced into a natural environment. Where there are no agents present able to biodegrade it, its concentration can increase as it passes up the food chain and higher organisms may suffer toxic effects. This phenomenon may be employed beneficially for the removal of toxic metals from wastewater, and for bioremediation. See: biosorbents.

bio-assay 1. The assessment of a substance's activity on living cells or on organisms. Animals have been used extensively in drug research in bio-assays in the pharmaceutical and cosmetics industries. Current trends are to develop bio-assays using bacteria or animal or plant cells, as these are easier to handle than whole animals or plants, are cheaper to make and keep, and avoid the ethical problems associated with testing of animals. 2. An indirect method to detect sub-measurable amounts of a specific substance by observing a sample's influence on the growth of live material.

bio-augmentation Increasing the activity of bacteria that decompose pollutants; a technique used in bioremediation.

bioavailability The proportion of a nutrient or administered drug etc. that can be taken up by an organism in a biologically effective form. For example, some soils high in phosphorus have a low level of P availability because the pH of the soil renders much of the P insoluble.

biocatalysis The use of enzymes to improve the efficiency of chemical reactions.

biochip See: DNA chip.

biocontrol Pest control by biological means. Any process using deliberately introduced living organisms to restrain the growth and development of other organisms, such as the introduction of predatory insects to control an insect pest. Synonym: biological control.

bioconversion Conversion of one chemical into another by living organisms, as opposed to their conversion by isolated enzymes or fixed cells, or by chemical processes. Particularly useful for introducing chemical changes at specific points in large and complex molecules.

biodegradable Capable of being biodegraded.

biodegrade The breakdown by micro-organisms of a compound to simpler chemicals. Materials that are easily biodegraded are colloquially termed biodegradable.

biodesulphurization The removal of organic and inorganic sulphur from coal by bacterial and soil micro-organisms. Certain bacteria can oxidize insoluble sulphur compounds into soluble sulphates, which can be washed away with the bacteria. See: bioleaching.

biodiversity The variability among living organisms from all sources, including, inter alia, terrestrial, marine and other ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems. Synonyms: biological diversity, ecological diversity.

bio-energetics The study of the flow and the transformation of energy that occur in living organisms.

bio-engineering The use of artificial tissues, organs and organ components to replace parts of the body that are damaged, lost or malfunctioning.

bio-enrichment Adding nutrients or oxygen to increase microbial breakdown of pollutants.

bio-ethics The branch of ethics that deals with the life sciences and their potential impact on society.

biofilms A layer of micro-organisms growing on a surface, in a bed of polymeric material which they themselves have made. Biofilms tend to form wherever a surface on which bacteria can grow is exposed to some suitable medium and a supply of bacteria.

biofuel A gaseous, liquid or solid fuel derived from a biological source, e.g. ethanol, rapeseed oil or fish liver oil.

biogas A mixture of methane and carbon dioxide resulting from the anaerobic decomposition of waste such as domestic, industrial and agricultural sewage.

bio-informatics The use and organization of information of biological interest. In particular, concerned with organizing bio-molecular databases (particularly DNA sequences), utilizing computers for analysing this information, and integrating information from disparate biological sources. See: in silico.

bioleaching The recovery of metals from their ores, using the action of micro-organisms, rather than chemical or physical treatment. For example, Thiobacillus ferroxidans has been used to extract gold from refractory ores. See: biorecovery.

biolistics A technique to generate transgenic cells, in which DNA-coated small metal particles (tungsten or gold) are propelled by various means fast enough to puncture target cells. Provided that the cell is not irretrievably damaged, the DNA is frequently taken up by the cell. The technique has been successfully used to transform animal, plant and fungal cells, and even mitochondria inside cells. Synonym: microprojectile bombardment.

biological ageing See: senescence.

biological containment Restricting the movement of organisms from the laboratory. Can take two forms: making the organism unable to survive in the outside environment, or making the outside environment inhospitable to the organism. For micro-organisms, the favoured approach is to engineer organisms to require a supply of a specific nutrient that is usually available only in the laboratory. For higher organisms (plants and animals), it is more possible to ensure that the outside environment is unsuited to growth, spread and reproduction.

biological control See: biocontrol.

biological diversity See: biodiversity.

biological oxygen demand (Abbreviation: BOD). The dissolved oxygen required for the respiration of a population of aerobic organisms present in water. Expressed in terms of the oxygen consumed in water at a temperature of 20°C per unit time. The BOD is used as an indication of the degree to which the sample of water is polluted, particularly by inorganic nutrients for plants.

biologics Agents, such as vaccines, that give immunity to diseases or harmful biotic stresses.

bioluminescence The enzyme-catalyzed production of light by a number of diverse organisms (e.g. fireflies and many deep ocean marine organisms). Utilized as a reporter gene in plant transgenesis, and for the detection of food-borne pathogenic bacteria.

biomagnification See: bio-accumulation.

biomass 1. The cell mass produced by a population of living organisms. 2. The organic matter that can be used either as a source of energy or for its chemical components. 3. All the organic matter that derives from the photosynthetic conversion of solar energy.

biomass concentration The amount of biological material in a specific volume.

biome A major ecological community or complex of communities, extending over a large geographical area and characterized by a dominant type of vegetation.

biometry The application of statistical methods to the analysis of continuous variation in biological systems. Synonym: biometrics.

biomimetic materials Employed to describe synthetic analogues of natural materials with advantageous properties. For instance, some synthetic molecules act chemically like natural proteins, but are not as easily degraded by the digestive system. Other systems such as reverse micelles and/or liposomes exhibit certain properties that mimic certain aspects of living systems.

biopesticide A compound that kills organisms by virtue of specific biological effects rather than as a broader chemical poison. Differ from biocontrol agents in being passive agents, whereas biocontrol agents actively seek the pest. The rationale behind replacing conventional pesticides with biopesticides is that the latter are more likely to be selective and biodegradable.

biopharming The use of genetically transformed crop plants and livestock animals to produce valuable compounds, especially pharmaceuticals. Synonym: molecular pharming.

biopiracy The patenting of genetic stocks, and the subsequent privatization of genetic resources collections. The term implies a lack of consent on the part of the originator.

biopolymer Any large polymer (protein, nucleic acid, polysaccharide) produced by a living organism. Includes some materials (such as polyhydroxybutyrate) suitable for use as plastics. Synonym: biological polymer.

bioprocess Any process that uses complete living cells or their components (e.g. enzymes, chloroplasts) to effect desired physical or chemical changes.

bioreactor A tank in which cells, cell extracts or enzymes carry out a biological reaction. Often refers to a fermentation vessel for cells or micro-organisms.

biorecovery The use of micro-organisms for the recovery of valuable materials (metals or particular organic compounds) from complex mixtures. See: biodesulphurization, bioleaching.

bioremediation A process that uses living organisms to remove contaminants, pollutants or unwanted substances from soil or water. See: remediation, bio-accumulation, bio-augmentation.

biosafety Referring to the avoidance of risk to human health and safety, and to the conservation of the environment, as a result of the use for research and commerce of infectious or genetically modified organisms.

biosafety protocol An inteRNAtionally agreed protocol set up to protect biological diversity from the potential risks posed by the release of genetically modified organisms. It establishes a procedure for ensuring that countries are provided with the information necessary to make informed decisions before agreeing to the import of such organisms into their territory. Synonym: Cartagena protocol. See: Convention on biological diversity.

biosensor A device that uses an immobilized biologically-related agent (such as an enzyme, antibiotic, organelle or whole cell) to detect or measure a chemical compound. Reactions between the immobilized agent and the molecule being analysed are converted into an electric signal.

biosilk A biomimetic fibre produced by the expression of the relevant orb-weaving spider genes in yeast or bacteria, followed by the spinning of the expressed protein into a fibre.

biosorbents Micro-organisms which, either by themselves or in conjunction with a substrate are able to extract and/or concentrate a desired molecule by means of its selective retention. See: bio-accumulation.

biosphere The part of the earth and its atmosphere that is inhabited by living organisms.

biosynthesis Synthesis of compounds by living cells, which is the essential feature of anabolism.

biosynthetic antibody binding sites (Abbreviation: BABS). See: dAb.

biotechnology 1. "Any technological application that uses biological systems, living organisms, or derivatives thereof, to make or modify products or processes for specific use" (Convention on Biological Diversity). 2. " Interpreted in a narrow sense, ..... a range of different molecular technologies such as gene manipulation and gene transfer, DNA typing and cloning of plants and animals" (FAO's statement on biotechnology)

biotic factor Other living organisms that are a component of an organism's environment, and form the biotic environment, affecting the organism in many ways.

biotic stress Stress resulting from attack by pathogenic organisms.

biotin A vitamin of the B complex, it acts as a co-enzyme for various enzymes that catalyse the incorporation of carbon dioxide into various compounds, and is essential for the metabolism of fats. Adequate amounts are normally produced by the intestinal bacteria in animals. Significant as a molecular biology reagent due to its high affinity with avidin and streptavidin. Synonym: vitamin H.

biotin labelling The attachment of biotin to another molecule, especially DNA.

biotinylated-DNA A DNA molecule labelled with biotin by incorporation of a biotinylated nucleotide (usually uracil) into a DNA molecule. The detection of the labelled DNA is achieved by complexing it with streptavidin to which is attached a colour-generating agent such as horseradish peroxidase that gives a fluorescent green colour upon reaction with various organic reagents.

biotope A small habitat in a large community.

biotoxin A naturally produced compound which shows pronounced biological activity, toxic to some or many organisms.

biotransformation The conversion of one chemical or material into another using a biological catalyst: a near synonym is biocatalysis, and hence the catalyst used is called a biocatalyst. Usually the catalyst is an enzyme, or a fixed whole, dead micro-organism that contains an enzyme or several enzymes.

bivalent Two paired homologous chromosomes (one of maternal origin; the other of paternal origin) at prophase to anaphase of the first meiotic division. Because DNA is replicated in prophase, each duplicated chromosome comprises two chromatids, and thus a bivalent comprises four chromatids.

blast cell A large, rapidly dividing cell that develops from a B cell in response to an antigenic stimulus. The blast cell then becomes an antibody-producing plasma cell.

blastocyst A mammalian embryo (fertilized ovum) in the early stages of development, approximately up to the time of implantation. It consists of a hollow ball of cells.

blastomere Any one of the cells formed from the first few cleavages in animal embryology. The embryo usually divides into two, then four, then eight blastomeres, and so on.

blastula In animals, an early embryo form that follows the morula stage; typically, a single-layered sheet (blastoderm) or ball of cells (blastocyst).

bleeding 1. Collection of blood from immunized animals. 2. Used to describe the occasional purplish-black colouration of media due to phenolic products given off by (usually fresh) transfers.

blot As a verb, to transfer DNA, RNA or protein to an immobilizing matrix. As a noun, the immobilizing matrix carrying DNA, RNA or protein. The various types of blot are named according to the probe and/or the probed molecules: Southern blot (DNA/DNA), northern blot (DNA/mRNA), western blot (antibody/protein), southwestern blot (DNA/protein). Only "Southern" is written with an initial capital, as it is named after Ed Southern, the inventor of the technique.

blunt end The end of a double-stranded DNA molecule in which neither strand extends beyond the other. Synonym: flush end.

blunt-end cut To cut a double-stranded DNA with a restriction endonuclease which generates blunt ends. Synonym: flush-end cut.

blunt-end ligation The joining of two blunt-ended double-stranded DNA molecules.

BOD Abbreviation for biological oxygen demand.

boring platform Sterile bottom half of a Petri dish used for preparing explants with a cork borer.

bound water Cellular water not released into the intercellular space upon freezing and thawing. Opposite: free water.

bovine growth hormone See: bovine somatotrophin

bovine somatotrophin (Abbreviation: BST) A natural protein in cattle. It has been cloned, using recombinant DNA technology, expressed in large amounts and marketed as an agricultural product to improve the growth rate and protein:fat ratios in farm cattle, and to improve milk yield. Its use is banned in some countries. Synonyms: bovine growth hormone.

bovine somatotropin See: bovine somatotrophin.

bovine spongiform enecelophalopathy (Abbreviation: BSE) Cattle disease (colloquially called mad cow disease) caused by proteinaceous infectious particles.

bp Abbreviation for base pair.

bract A modified leaf that subtends flowers or inflorescences and may appear to be a petal.

breed 1.a sub-specific group of domestic livestock with definable and identifiable external characteristics that enable it to be separated by visual appraisal from other similarly defined groups within the same species. 2. a group of domestic livestock for which geographical and/or cultural separation from phenotypically similar groups has led to acceptance of its separate identity.

breed at risk An animal breed that is in danger of becoming extinct because its population has fallen below a critical number.

breeding The process of sexual reproduction and production of offspring.

breeding value A quantitative genetics term, describing that part of the deviation of an individual phenotype from the population mean that is due to the additive effects of alleles. Thus, if an individual is mated with a random sample of individuals from a population, its breeding value for a given trait is twice the average deviation of its offspring from the population mean for that trait.

brewer's yeast Strains of the yeast Saccharomyces cerevisiae that are used for the production of beer.

bridge A filter paper or other substrate used as a wick and support structure for a plant tissue in culture when a liquid medium is used.

broad-host-range plasmid A plasmid that can replicate in a number of different bacterial species.

broad-sense heritability The proportion of the total phenotypic variation which results from genetic variation or interaction between the genotype and the environment.

broodstock The group of males and females from which fish are bred.

browning Discolouration of freshly cut surfaces of plant tissue due to phenolic oxidation. In plant tissue culture, it may indicate a nutritional or pathogenic problem, generally leading to necrosis.

BSA Abbreviation for bovine serum albumin.

BSE Abbreviation for bovine spongiform encephalopathy. See proteinaceous infectious particle.

BST Abbreviation for bovine somatotrophin.

Bt Abbreviation for Bacillus thuringiensis.

bubble column fermenter A bioreactor in which the cells or micro-organisms are kept suspended in a tall cylinder by rising air, which is introduced at the base of the vessel.

bud A region of meristematic tissue with the potential for developing into leaves, shoots, flowers or combinations of these; generally protected by modified scale leaves.

bud sport A somatic mutation arising in a bud, generating a genetically different shoot. Includes changes due to gene mutation, chromosomal mutation or polyploidy.

budding 1. A method of asexual reproduction in which a new individual is derived from an outgrowth (bud) that becomes detached from the body of the parent. 2. Among fungi, budding is characteristic of the brewers yeast Saccharomyces cerevisiae. 3. A form of graft in which a single vegetative bud is taken from one plant and inserted into stem tissue of another plant so that the two will grow together. The inserted bud develops into a new shoot.

bulked segregant analysis A method to obtain markers linked to a target trait, in which DNA samples, prepared from a number of individuals of each of two contrasting phenotypes, are separately pooled and used to generate contrasting DNA fingerprints. DNA fragments unique to one pool become candidates for a marker linked to the gene controlling the trait.

buoyant density The intrinsic density which a molecule, virus or sub-cellular particle has when suspended in an aqueous solution of a salt, such as CsCl, or a sugar, such as sucrose. DNA from different species has different characteristic buoyant densities, determined largely by the relative proportion of the base-pairs G+C, to A+T.

C Abbreviation for cytosine.

CAAT box A conserved DNA sequence found within the promoter region of the protein-encoding genes of many eukaryotic organisms. So-called because of its consensus sequence GGCCAATCT, it occurs around 75 bases prior to the transcription initiation site; and is one of several sites for the recognition and binding of transcription factors. Synonym: CAT box.

cabinet See: growth cabinet.

callipyge An inherited trait in livestock (e.g. sheep) that results in thicker, meatier hind-quarters, and hence a higher meat yield per animal.

callus (pl.: calli) A protective tissue, consisting of parenchyma cells, that develops over a cut or damaged plant surface. 2. Mass of undifferentiated, thin-walled parenchyma cells induced by hormone treatment. 3. Actively dividing non-organized masses of undifferentiated and differentiated cells often developing from injury (wounding) or in tissue culture in the presence of growth regulators.

callus culture A technique of plant tissue culture, usually on solidified medium and initiated by inoculation of small explants. Used as the basis for organogenic (shoot or root forming) cultures, cell cultures or proliferation of embryoids. Callus cultures can be indefinitely maintained through regular sub-culturing.

cambial zone Region in stems and roots consisting of the cambium and its recent derivatives.

cambium (pl.: cambia) A one or two cells thick layer of plant meristematic tissue, between the xylem and phloem tissues, which gives rise to secondary tissues, thus resulting in an increase in the diameter of the stem or root. The two most important cambia are the vascular (fascicular) cambium and the cork cambium.

cAMP Abbreviation for cyclic adenosine monophosphate.

CaMV Abbreviation for cauliflower mosaic virus.

CaMV 35S Abbreviation for cauliflower mosaic virus 35S ribosomal DNA promoter. See: cauliflower mosaic virus.

candidate gene A gene whose deduced function (on the basis of DNA sequence) suggests that it may be involved in the genetic control of an aspect of phenotype.

candidate-gene strategy An experimental approach in which knowledge of the biochemistry and/or physiology of a trait is used to identify candidate genes. Synonym: functional gene cloning.

canola A specific subgroup of oilseed rape cultivars; canola oil is the highly mono-unsaturated fatty acid and low in erucic acid product produced in the seed of these cultivars.

cap The structure found on the 5´-end of eukaryotic mRNA, and consisting of an inverted, methylated guanosine residue. See G cap, cap site.

CAP Abbreviation for catabolite activator protein.

cap site The site on a DNA template where transcription begins. It corresponds to the nucleotide at the 5' end of the RNA transcript which accepts the G cap.

capacitation The final stage, inside the female genital tract, in the maturation process of a spermatozoon, as it penetrates the ovum.

capillary electrophoresis A form of electrophoresis used widely in current large-scale DNA sequencing facilities, where the sample is passed through a long, very-narrow-bore tube containing a re-usable matrix.

CAPS See: cleaved amplified polymorphic sequence.

capsid The protein coat of a virus. The capsid often determines the shape of the virus. Synonym: coat protein.

capsule Carbohydrate coverings that have antigenic specificity, present on some types of bacteria and other micro-organisms. The capsule is usually composed of polysaccharides, polypeptides, or polysaccharide-protein complexes. These materials are arranged in a compact manner around the cell surface.

carbohydrate See: polysaccharide.

carboxypeptidase A class of enzymes which catalyse the cleavage of peptide bonds, requiring a free carboxyl group in the substrate. The peptide bond adjacent to this group is cleaved and a free amino acid is released. Used for deriving the amino acid sequence of peptides.

carcinogen A substance capable of inducing cancer in an organism.

carcinoma A malignant tumour derived from epithelial tissue, which forms the skin and the outer cell layers of internal organs.

carotene A reddish-orange plastid pigment involved in photosynthesis. A carotenoid and precursor of vitamin A.

carotenoid A group of chemically similar red to yellow pigments responsible for the characteristic colour of many plant organs or fruits, such as tomatoes, carrots, etc. Oxygen-containing carotenoids are called xanthophylls. Carotenoids serve as light-harvesting molecules in photosynthetic assemblies and also play a role in protecting prokaryotes from the deleterious effects of light. See: carotene.

carpel Female reproductive organ of flowering plants, consisting of stigma, style and ovary.

carrier A heterozygous individual bearing a recessive mutant allele for a defective condition that is "masked" by the presence of the dominant normal allele; the phenotype is normal, but the individual passes the defective (recessive) allele to half of its offspring.

carrier DNA DNA of undefined sequence which is added to the transforming (plasmid) DNA used in physical DNA-transfer procedures. This additional DNA increases the efficiency of transformation in electroporation and chemically-mediated DNA delivery systems. The mechanism responsible is not known.

carrier molecule 1. A molecule that plays a role in moving electrons through the electron transport chain. They are usually proteins bound to non-protein groups and able to undergo oxidation and reduction relatively easily, thus allowing electrons to flow. 2. A lipid-soluble molecule that can bind to lipid-insoluble molecules and transport them across membranes. Carrier molecules have specific sites that interact with the molecules they transport. The efficiency of carrier molecules may be modified by changing the interacting sites through genetic engineering.

Cartagena protocol See: biosafety protocol.

casein A group of milk proteins.

casein hydrolysate The mixture of amino acids and peptides produced by enzymatic or acid hydrolysis of casein.

cassette See: construct.

CAT box See: CAAT box.

catabolic pathway A pathway by which an organic molecule is degraded in order to release energy for growth and other cellular processes.

catabolism The breakdown of large molecules in living organisms, with the accompanying release of energy.

catabolite activator protein (Abbreviation: CAP). A protein which combines with cyclic AMP. The cAMP-CAP complex binds to the promoter regions of E. coli and stimulates transcription of the relevant operon. Synonyms: catabolite regulator protein (CRP), cyclic AMP receptor protein.

catabolite repression Glucose-mediated reduction in the rates of transcription of genes that encode enzymes involved in catabolic pathways (e.g. the lac operon).

catalase A metalloenzyme, present in both plants and animals, that catalyzes the decomposition of hydrogen peroxide to water and oxygen. This activity is important in the detoxification of reactive oxygen generated as part of the response to stress.

catalysis The process of increasing the rate of a chemical reaction by the addition of a substance that is not itself changed by the reaction (the catalyst).

catalyst A substance that promotes a chemical reaction by lowering the activation energy of a chemical reaction, without itself undergoing any permanent chemical change.

catalytic antibody An antibody selected for its ability to catalyse a chemical reaction by binding to and stabilizing the transition-state intermediate. Synonym: abzyme.

catalytic RNA See: ribozyme.

catalytic site The part of the surface of an enzyme molecule (usually only a small portion of the total) necessary for the catalytic process.

cauliflower mosaic virus (Abbreviation CaMV). A DNA virus affecting cauliflower and many other dicot species. Its importance is due to the promoter of its 35S ribosomal DNA, which is constitutively active in most plant tissues, and has therefore been widely used as a promoter for the expression of transgenes.

cauliflower mosaic virus 35S promoter (Abbreviation CaMV 35S). A promoter sequence isolated from the ribosomal gene of the cauliflower mosaic virus

caulogenesis Stem organogenesis; induction of shoot development from callus.

CBD Abbreviation for Convention on Biological Diversity.

ccc DNA Abbreviation for covalently-closed circle DNA. See: circularization.

CD molecules Abbreviation for: cluster of differentiation molecules. Any group of surface antigens associated with a specific sub-population of T cells.

cDNA Abbreviation for complementary DNA.

cDNA clone A double-stranded cDNA molecule propagated in a vector, and used as a probe in RFLP analyses, as template for the production of EST sequences, and for gene expression studies.

cDNA cloning A method of cloning the coding sequence of a gene, starting with its mRNA transcript.

cDNA library An collection of cDNA clones.

CDR Abbreviation for complementarity-determining regions.

cell The fundamental level of structural organization in complex organisms. Eukaryotic cells contain a nucleus (with chromosomes) and cytoplasm with the protein synthesis machinery, bounded by a membrane. Prokaryotic cells have no nucleus.

cell culture The in vitro growth of cells isolated from multi-cellular organisms.

cell cycle The sequence of stages that a cell passes through between one division and the next. The cell cycle oscillates between mitosis (M) and the interphase, which is divided into the G₁ phase (involving a high rate of biosynthesis and growth), the S phase (in which the DNA content is doubled as a consequence of chromosome replication), and the G₂ phase (preparatory for cell division).

cell differentiation The transition of cells (by the programmed activation and de-activation of the necessary genes) from an tissue-unspecific type, in which daughter cells are similarly undifferentiated, to a committed type in which the cell line specializes to become a recognizable tissue or organ.

cell division Formation of two or more daughter cells from a single parent cell. The nucleus divides first, followed by the formation of a cell membrane between the daughter nuclei. Division of somatic cells is termed mitosis; egg and sperm precursors are formed following meiosis.

cell fusion Formation in vitro of a single hybrid cell from the coalescence of two cells of different species origin. In the hybrid cell, the donor nuclei may remain separate, or may fuse, but during subsequent cell divisions, a single spindle is formed so that each daughter cell has a single nucleus containing complete or partial sets of chromosomes from each parental line. Synonym: cell hybridization.

cell generation time The interval between the beginning of consecutive divisions of a cell, equivalent to the time that it takes for a population of single-celled organisms to double its cell number.

cell hybridization See: cell fusion.

cell line 1. A cell lineage that can be maintained in vitro. Significant genetic changes can occur during lengthy periods in culture, so that the genotype of long-term cell lines may not be the same as that of the starter cell. 2. A cell lineage that can be recognized in vivo.

cell membrane See: plasmalemma.

cell number The number of cells per unit volume of a culture.

cell plate The precursor of the cell wall, formed at the beginning of cell division. The cell plate develops in the region of the equatorial plate and arises from membranes in the cytoplasm.

cell sap Water and dissolved substances, sugar, amino acids, waste substances, etc., in the plant cell vacuole.

cell selection The process of selecting cells exhibiting specific traits within a group of genetically different cells. Selected cells are often sub-cultured onto fresh medium for continued selection and exposed to an increased level of the selection agent to eliminate false positives.

cell sorter See: fluorescence-activated cell sorting, flow cytometry.

cell strain An in vitro culture initiated by asexual reproduction from a single cell. Such cell lines should represent a population of genetically homogenous cells. Strains are defined by specific properties or markers used for their selection. Synonym: single-cell line.

cell suspension Cells in culture in moving or shaking liquid medium, often used to describe suspension cultures of single cells and cell aggregates.

cell wall A rigid external structure which surrounds plant cells. It is formed outside the plasmalemma and consists primarily of cellulose.

cell-free protein synthesis See: in vitro translation.

cell-free transcription See: in vitro transcription.

cell-free translation See: in vitro translation.

cell-mediated (cellular) immune response See: T-cell-mediated (cellular) immune response.

cellular oncogene See: proto-oncogene.

cellulase Enzyme catalysing the breakdown of cellulose.

cellulose A complex polysaccharide composed of long linear chains of glucose residues. It comprises 40% to 55% by weight of the plant cell wall.

cellulose nitrate See: nitrocellulose.

cellulosome A multi-protein aggregate present in some micro-organisms which degrade cellulose. It contains multiple copies of the enzymes necessary for this process, and is often found on the outer surface of the micro-organism cell.

centiMorgan (Abbreviation: cM). Unit of map distance. For small recombination fractions, cM and % recombination frequency are equivalent.

central dogma The basic concept that, in nature, genetic information generally flows from DNA to RNA to protein. However, information contained in the RNA molecules of retroviruses can also flow back to DNA.

central mother cell A subsurface cell located in a plant apical meristem and characterized by a large vacuole.

centre of origin The geographic locations where a particular domesticated plant species originated. These areas are the likeliest source of natural genetic variation, and represent ideal targets for in situ conservation.

centrifugation Separating molecules by size or density using centrifugal forces generated by a spinning rotor. G-forces of several hundred thousand times gravity are generated in ultracentrifugation. See: density gradient centrifugation.

centrifuge A mechanical device which delivers the centrifugal forces necessary for centrifugation.

centriole An organelle in many animal cells that appears to be involved in the formation of the spindle during mitosis. During cell division, the two centrioles move to opposite sides of the nucleus to form the ends of the spindle.

centromere The eukaryotic chromosome structure, which appears as a constriction in karyotype analysis, to which the spindle fibres attach during mitotic and meiotic division. Composed of highly repetitive DNA.

centrosome A specialized region of a living cell, situated next to the nucleus, where microtubules are assembled and broken down during cell division. The centrosome of most animal cells contains a pair of centrioles.

cephem-type antibiotic An antibiotic that shares the basic chemical structure of cephalosporin.

chain terminator 1. See: stop codon. 2. In the Sanger method of DNA sequencing, refers to the labelled di-deoxynucleotide triphosphates which are added to disrupt DNA polymerase extension.

Chakrabarty decision A landmark legal case in the U.S.A., in which it was held that the inventor of a new micro-organism whose invention otherwise met the legal requirements for obtaining a patent, could not be denied a patent solely because the invention was alive. This has set the precedent for the patenting of life forms.

chaperone A family of proteins that ensure the correct assembly and conformation of other polypeptides in vivo as they emerge from the ribosome, but are not themselves components of the functional assembled structures. The prokaryotic equivalents are known as chaperonins. See: heat shock protein.

chaperonin See: chaperone.

character See: trait.

characterization Description of the essential properties of an organism or system.

charcoal The black porous residue of partly burnt wood, bones, etc; a form of carbon. See: activated charcoal

chelate A cation bound to an organic molecule through electron pair donation from nitrogen and/or oxygen atoms in its structure. Ethylenediamine tetraacetic acid is a typical and frequently employed chelating agent. Soluble chelates can supply plants with micronutrients which would otherwise be unavailable because of precipitation.

chemical mutagen A chemical capable of inducing mutations in living organisms.

chemically-defined medium When all of the chemical components of a culture medium are fully known and defined.

chemiluminescence The emission of light during the course of a chemical reaction.

chemostat A continuous and open culture in which growth rate and cell density are maintained constant by a fixed rate of input of a growth-limiting nutrient.

chemotaxis The movement of a cell, or the whole or part of an organism, towards or away from an increasing concentration of a particular substance.

chemotherapy The treatment of disease, especially infections or cancer, by means of chemicals.

chiasma (pl.: chiasmata) A visible point of junction between two non-sister chromatids of homologous chromosomes during the first meiotic prophase. Synonym: cross-over.

chimera (or chimaera) 1. An organism whose cells are not all genotypically identical. This can occur as a result of: somatic mutation; grafting (see: graft chimera); or because the individual is derived from two or more embryos or zygotes. 2. A recombinant DNA molecule that contains sequences from different organisms.

chimeraplasty A method designed to create defined alterations in DNA sequence at a target locus, with potential both for gene therapy and for investigating gene function. A synthetic nucleic acid that contains DNA interspersed with small amounts of RNA is introduced into the target cell, where it pairs with its target gene sequence and then triggers the cell's DNA repair machinery, resulting in the replacement of the native sequence by the synthetic one.

chimeric DNA See: chimera (2).

chimeric gene An engineered gene, where a coding sequence is fused to promoter and/or other sequences derived from a different gene. Most genes used in transformation are chimeric. Synonym: fusion gene.

chimeric protein See: fusion protein.

chimeric selectable marker gene A gene that is constructed from parts of two or more different genes and allows the host cell to survive under conditions where it would otherwise die.

chip See: micro-array.

chitin A nitrogenous polysaccharide that gives structural strength to the exoskeleton of insects and the cell walls of fungi.

chitinase An enzyme which breaks down chitin.

chloramphenicol An antibiotic that interferes with protein synthesis.

chlorenchyma Plant tissue (leaf mesophyll and other parenchyma cells) containing chloroplasts.

chlorophyll One of the two pigments responsible for the green colour of most plants. It is an essential component of the machinery to absorb light energy for photosynthesis. See: chloroplast.

chloroplast Specialized plastid that contains chlorophyll. Lens-shaped and bounded by a double membrane, chloroplasts contain membranous structures (thylakoids) piled up into stacks, surrounded by a gel-like matrix (stroma). They are the site of solar energy transfer and some important reactions involved in starch or sugar synthesis. Chloroplasts have their own DNA; these genes are inherited only through the female parent, and are independent of nuclear genes.

chloroplast DNA The DNA present in the chloroplast. Although the chloroplast has a small genome, the large number of chloroplasts per cell ensures that chloroplast DNA is a significant proportion of the total DNA in a plant cell.

chloroplast transit peptide (Abbreviation: CTP). A transit peptide that, when fused to a protein, acts to transport that protein into plant chloroplasts. Once inside the chloroplast, the transit peptide is cleaved off the protein. Used to target transgene expression to the chloroplast, where this is appropriate.

chlorosis The appearance of yellow colour in plants, due to the failure of development or the breakdown of chlorophyll. This is generally a symptom of either nutritional disturbance or of pathogen infection.

chromatid Each of the two strands of chromatin comprising a duplicated chromosome. The term is applied only while the two chromatids are joined at the centromere. As soon as the centromere divides, setting the two chromatids adrift (during anaphase of mitosis; and during anaphase II of meiosis), they are called chromosomes.

chromatin Substance of which eukaryotic chromosomes are composed. It consists of a complex of DNA, histone and non-histone chromosomal proteins (mainly histones), and a small amount of RNA.

chromatin fibre The standard structural conformation of chromatin in strands of 30 nm average diameter.

chromatography A method for separating the components of mixtures of molecules by partitioning them between two phases, one stationary and the other mobile. Appropriate selection of partitioning mechanism can produce separation of very closely-related molecules.

chromocentre Body produced by fusion of the heterochromatic regions of the chromosomes in the polytene tissues (e.g. the salivary glands) of certain Diptera.

chromogenic substrate A compound or substance that contains a colour-forming group.

chromomeres Small dense bodies identified by their characteristic size and linear arrangement along a chromosome.

chromonema (pl.: chromonemata) An optically single thread forming an axial structure within each chromosome.

chromoplast Plastid containing pigments other than chlorophyll. See: chloroplast.

chromosomal aberration An abnormal change in chromosome structure or number, including deficiency, duplication, inversion, translocation, aneuploidy, polyploidy, or any other change from the normal pattern.. Although it can be a mechanism for enhancing genetic diversity, most alterations are fatal or debilitating, especially in animals. See: chromosome mutation.

chromosomal integration site A chromosomal location where foreign DNA can be integrated, often without impairing any essential function in the host organism.

chromosomal polymorphism The occurrence of one to several chromosomes in two or more alteRNAtive structural forms within a population; the structurally changed chromosomes are the result of chromosome mutations (i.e. any structural change involving the gain, loss or re-location of chromosome segments).

chromosome In eukaryotic cells, chromosomes are the nuclear bodies containing most of the genes largely responsible for the differentiation and activity of the cell. Chromosomes are most easily studied in their contracted state, which occurs around the metaphase of mitosis or meiosis; they contain most of the cell's DNA in the form of chromatin. Each eukaryotic species has a characteristic number of chromosomes. Bacterial and viral cells contain only one chromosome, which consists of a single or double strand of DNA or, in some viruses, RNA, without histones.

chromosome aberration See: chromosomal aberration.

chromosome banding Differential staining of chromosomes in such a way that light and dark areas occur along the length of the chromosomes in repeatable patterns. Identical banding pattern implies chromosome homology.

chromosome jumping A technique that allows two segments of duplex DNA that are separated by thousands of base pairs (about 200 kb) to be cloned together. After sub-cloning, each segment can be used as a probe to identify cloned DNA sequences that, at the chromosome level, are roughly 200 kb apart. See positional cloning.

chromosome landing An alteRNAtive to chromosome walking for positional cloning. Clones of genomic DNA are fragmented so as to include both the target gene and a closely linked marker and are screened to select ('land on') those clones that contain the target gene.

chromosome mutation A change in the gross structure of a chromosome, usually causing severely deleterious effects in the organism, but can be maintained in a population (See: chromosomal polymorphism). They are often due to meiotic errors. The main types of chromosome mutation are translocation, duplication, s and inversion.

chromosome theory of inheritance The theory that chromosomes carry the genetic information and that their behaviour during meiosis provides the physical basis for segregation and independent assortment.

chromosome walking A strategy for mapping or sequencing a chromosome segment and for positional cloning. Large restriction fragments (or BAC clones) are generated and, after probing, a single starting point is identified. New probes are synthesized complementary to sequences of the same fragment (BAC clone) that are adjacent to the starting point, and these are then used to identify different restriction fragments (BAC clones) overlapping the one selected as the starting point. The procedure is used repetitively, working away from the starting point.

chymosin An enzyme that clots milk, used in the manufacture of cheese.

ciliate (adj.) See cilium.

cilium (pl.: cilia) Hairlike locomotor structure on certain cells; a locomotor structure on a ciliate protozoan.

circadian Of physiological activity, etc.: recurring at approximately 24-hour intervals.

circularization The self-ligation of a linear DNA fragment having complementary ends, generally generated by digestion with a restriction endonuclease. Successful ligation produces a molecule in the form of a covalently-closed circle. Plastid DNA and plasmids are examples of naturally circularized DNA.

cis configuration See: coupling.

cis heterozygote A double heterozygote that contains two mutations arranged in a cis configuration (e.g. a+ b+ / a b).

cis-acting protein A protein with the particular property of acting only on the molecule of DNA from which it was expressed.

cis-acting sequence A nucleotide sequence that only affects the expression of genes located on the same chromosome.

cistron A DNA sequence that codes for a specific polypeptide; a gene.

class switching The process during which a plasma cell stops producing antibodies of one class and begins producing antibodies of another class.

cleave To break phosphodiester bonds of double-stranded DNA, usually with a type II restriction endonuclease. Synonyms: cut; digest.

cleaved amplified polymorphic sequence A segment of DNA that can be amplified by polymerase chain reaction (PCR) and which contains a DNA sequence polymorphism. Following PCR amplification of a locus, the amplicon is treated with a restriction endonuclease. If the recognition site for this enzyme is present in the amplicon, two or more restriction fragments are generated. Thus sequence variation between individuals at the recognition site(s) can be detected by electrophoresis. See also: restriction fragment length polymorphism.

cline Variation in one or more phenotypic characters or allele frequencies across a geographical gradient.

clonal propagation Asexual propagation of many new plants (ramets) from an individual (ortet); all have the same genotype.

clonal selection The production of a population of plasma cells all producing the same antibody in response to the interaction between a B lymphocyte producing that specific antibody and the antigen bound by that antibody. See: primary immune response, secondary immune response.

clone 1. A group of cells or individuals that are genetically identical as a result of asexual reproduction, breeding of completely inbred organisms, or forming genetically identical organisms by nuclear transplantation. 2. Group of plants genetically identical in which all are derived from one selected individual by vegetative propagation. 3. Verb: to clone. To insert a DNA segment into a vector or host chromosome.

clone bank See: gene bank.

cloned strain or line A strain or line descended directly from a clone.

cloning See: gene cloning.

cloning site See: insertion site.

cloning vector A small, self-replicating DNA molecule - usually a plasmid or viral DNA chromosome - into which foreign DNA is inserted in the process of cloning genes or other DNA sequences of interest. It can carry inserted DNA and be perpetuated in a host cell. Synonym: cloning vehicle.

cloning vehicle See: cloning vector.

closed continuous culture A culture system, in which the inflow of fresh medium is balanced by the outflow of corresponding volumes of spent medium. Cells are separated mechanically from outflowing medium and added back to the culture.

cluster of differentiation See: CD molecules.

cM Abbreviation for centiMorgan.

CMP Abbreviation for cytidine monophosphate. See: cytidylic acid.

coat protein See: capsid.

coccus A spherical bacterium.

co-cloning The unintentional cloning of DNA fragments, along with the desired one, that can occur when the source of DNA being cloned is not sufficiently purified.

coconut milk Liquid endosperm of the coconut, often used to supply organic nutrients to in vitro cultures of plant cells and tissues.

co-culture The joint culture of two or more types of cells, such as a plant cell and a micro-organism, or two types of plant cells. Used in various dual-culture systems or in nurse culture.

Codex Alimentarius Commission An international regulatory body (part of FAO) responsible for the definition of a set of international food standards. The Commission periodically determines, then publishes a list of food ingredients and maximum allowable levels (the Codex Alimentarius) deemed to be safe for human consumption.

coding The specification of a peptide sequence, by the code contained in DNA molecules. See: genetic code.

coding sequence That portion of a gene which directly specifies the amino acid sequence of its product. Non-coding sequences of genes include introns and control regions, such as promoters, operators, and terminators.

coding strand The strand of a DNA double helix that contains the same base sequence (after substituting U for T) found in the mRNA molecule resulting from transcription of that segment of DNA. Sometimes called the sense strand. The mRNA molecule is transcribed from the other strand, known as the template or antisense strand. See: antisense DNA.

co-dominance Where both alleles are expressed in the heterozygous state, so that the phenotype reflects a contribution from both alleles. For example, roan coat colour in cattle results from a mixture of red hairs and white hairs, caused by heterozygosity for the red allele and the white allele.

co-dominant alleles See: co-dominance.

codon One of the groups of three consecutive nucleotides in mRNA, which represent the unit of genetic coding by specifying a particular amino acid during the synthesis of polypeptides in a cell. Each codon is recognized by a tRNA carrying a specific amino acid, which is incorporated into a polypeptide chain during protein synthesis. In DNA, any informative triplet of bases, including both coding and control sequences. See: genetic code, start codon, stop codon. Synonym: triplet. See: annex 3.

codon optimization An experimental strategy in which codons within a cloned gene - ones not generally used by the host cell translation system - are changed by in vitro mutagenesis to the preferred codons, without changing the amino acids of the synthesized protein.

co-enzyme Synonym for co-factor.

co-evolution The evolution of complementary adaptations in two species brought about by the selection pressure that each exerts on the other. Common in symbiotic associations, in insect-pollinated plants, etc.

co-factor An organic molecule or inorganic ion necessary for the normal catalytic activity of an enzyme. Synonym: co-enzyme.

co-fermentation The simultaneous growth of two micro-organisms in one bioreactor.

cohesive end See: extension.

coincidence The ratio of the observed to the expected frequency of double cross-overs, where the expected frequency is calculated by assuming that the two cross-over events occur independently of one another.

co-integrate A chimeric DNA molecule formed by the incorporation at a single site of two different DNA molecules.

co-integrate vector system A two plasmid system for plant transgenesis. One plasmid is engineered to carry a T-DNA segment incorporating the gene(s) to be introduced. After introduction into Agrobacterium tumefaciens, the plasmid undergoes homologous recombination with a resident disarmed Ti plasmid to form a single plasmid carrying the genetic information for transferring the genetically engineered T-DNA region to plant cells.

colchicine An alkaloid, obtained from the autumn crocus Colchicum autumnale, which inhibits spindle formation. When applied during mitosis, chromosomes are unable to separate during anaphase. This property is used to achieve a doubling of the chromosome number. A further use is to halt mitosis at metaphase, the stage at which karyotypes are best viewed.

coleoptile Protective sheath covering the shoot apex of the embryo in the grasses.

coleorhiza A protective sheath surrounding the radicle in the grasses.

co-linearity 1. A general relationship in which the units in one molecule occur in the same sequence as the units in another molecule which they specify; e.g. the nucleotides in a gene are co-linear with the amino acids in its encoded polypeptide. 2. The phenomenon whereby gene order is preserved between distinct species.

collenchyma A tissue of living cells, found particularly in midribs and leaf petioles. Characterized by cell walls unevenly thickened with cellulose and hemicellulose, but never lignified; it functions as a mechanical support in young, short-lived or non-woody organs.

colony 1. An group of genetically identical cells or individuals derived from a single progenitor. 2. A group of interdependent cells or organisms.

colony hybridization A technique that uses a nucleic acid probe to identify a recombinant bacterial colony carrying a particular inserted DNA.

combinatorial library The many novel combinations (consisting of one heavy and one light immunoglobulin chain coding region) that are generated when a heavy-chain library is combined by random pairing with a light-chain library. These constructs are propagated in a vector, and their gene products screened for novel affinity properties.

combining site See: antibody binding site.

commensalism The interaction of two or more dissimilar organisms where the association is advantageous to one without affecting the other(s).

companion cell A living cell associated with the sieve cell of phloem tissue in vascular plants.

comparative mapping The comparison of map locations of genes and markers between species. In comparisons between closely related species, this will usually uncover a high degree of conservation of synteny and co-linearity. In these cases, the likely location of many genes can be predicted from model system data. Comparisons across wider phylogenetic distances reveal increasing loss of synteny.

comparative positional candidate gene Relates to an indirect means of assigning function to a QTL. Where a QTL has been linked to a marker in one species, and that same marker is linked to a known gene in a model system, inferences may be drawn as to the nature of the QTL.

competent 1. Bacterial cells able to take up foreign DNA molecules and thereby become genetically transformed. Can be genetically determined, or induced by physical treatment. 2. A competent cell is capable of developing into a fully functional embryo.

complement proteins Proteins that bind to antibody-antigen complexes and help degrade the complexes by proteolysis.

complementarity 1. See: complementary. 2. The similar correspondence between DNA and the mRNA transcribed from it.

complementarity-determining regions (Abbreviation: CDR). Regions of the light and heavy subunits of the immunoglobulin molecules that interact with the antigen. The primary amino acid sequences of these regions are highly variable between antibodies of the same class. See: antibody binding site.

complementary Two DNA molecules are complementary to one another when each successive base position from the 5' end in the first molecule is matched by the corresponding residue in the second, starting at the 3' end, according to the normal base pair rules (i.e. A for T, C for G). In the appropriate conditions, two complementary single-stranded DNA molecules will renature to form a double-stranded molecule. Complementary nucleotides are members of the pairs adenine-thymine, adenine-uracil, and guanine-cytosine that have the ability to hydrogen bond to one another.

complementary DNA (Abbreviation: cDNA). A DNA strand synthesized in vitro from a mature RNA template using reverse transcriptase. DNA polymerase is then used to create a double-stranded molecule. Differs from genomic DNA by the absence of introns. Synonym: copy DNA.

complementary entity 1. Synonym of base pair. 2. One of a pair of segments or strands of nucleic acid that will hybridize with one another.

complementary genes Two or more interdependent genes, such that (in the case of dominant complementarity) the dominant allele from either gene can only produce an effect on the phenotype of an organism if the dominant allele from the other gene is also present; in the case of recessive complementarity, only double homozygous recessive individuals show the effect.

complementary homopolymeric tailing The process of adding complementary nucleotide extensions to DNA molecules, (e.g. deoxyguanosine) to the 3' end of one DNA molecule and deoxycytidine to the 5' end of another DNA molecule) to facilitate the ligation of the two DNA molecules. Synonyms: dA - dT tailing, dG - dC tailing.

complementation See: genetic complementation.

complementation test A genetic method to test whether or not independent mutations are allelic. In a cross between the two mutant individuals, the genotype will be m₁m₂ if the mutations are allelic and m₁ +/+ m₂ if non-allelic. The phenotype of the former will be mutant, but that of the latter will be wild type (normal). Synonym: trans test.

complete digest The treatment of a DNA preparation with a restriction endonuclease for sufficient time for all of the potential target sites within that DNA to have been cleaved. Opposite: partial digest.

composite transposon A transposon formed when two identical or nearly identical transposons insert on either side of a non-transposable segment of DNA.

compound chromosome A chromosome formed by the fusion of two separate chromosomes, as in attached-X chromosomes or attached-X-Y chromosomes.

concatemer A DNA segment made up of repeated sequences linked head to tail.

concordance Identity of matched pairs or groups for a given trait, such as sibs expressing the same trait.

conditional lethal mutation A mutation that is lethal under one set of environmental conditions (the restrictive conditions, commonly associated with high temperature) but is viable under another set of environmental conditions (the permissive conditions).

conditioning 1. The effects on phenotypic characters of external agents during critical developmental stages. 2. The undefined interaction between tissues and culture medium resulting in the growth of single cells or small aggregates. Conditioning may be accomplished by immersing cells or callus contained within a porous material (such as dialysis tubing) into fresh medium for a period dependent on cell density and a volume related to the amount of fresh medium.

conformation The various three dimensional shapes that can be adopted by a given molecule. In particular, the different ways in which the primary sequence of a biological polymer may be folded. This is determined by intra-molecular forces, including hydrogen bonding and, in proteins, disulphide bridges. In proteins, conformation is often critical for biological activity, and the functions of some molecules are carried out by switching between two alternative stable conformations. The native conformation found in vivo may be changed to typically less ordered, uncharacterized, and usually biologically-inactive forms by denaturing.

conidium (pl.: conidia) An asexual spore produced by a specialized hypha in certain fungi.

conjugation 1. Union of gametes or unicellular organisms during fertilization. 2. The unidirectional transfer of plasmid DNA from one bacterium cell to another, involving cell-to-cell contact. The plasmid usually encodes the majority of the functions necessary for its own transfer. 3. Attachment of sugar and other polar molecules to less polar compounds, thus making them more water soluble.

conjugative functions Plasmid-based genes and their products that facilitate the transfer of a plasmid from one bacterium to another via conjugation.

consanguinity Related by descent from a common ancestor.

consensus sequence The part of a gene or signal sequence that is shared over a wide range of members of a gene family, both within a given species, or in comparisons between species.

conservation See: gene (resources) conservation, conserved sequence

conserved sequence An identical or highly similar sequence of nucleotides or amino acids which occurs as part, or all of a number of different genes or proteins, in either the same or different species. This conservation can signify which part of the full sequence is responsible for the functionality.

constant domains Regions of antibody chains that have the same amino acid sequence in different members of a particular class of antibody molecules.

constitutive The expression of a gene without any requirement for induction.

constitutive gene A gene that is continually expressed in all cells of an organism.

constitutive promoter An unregulated promoter that allows for continual transcription of its associated gene.

constitutive synthesis Continual synthesis of a gene product by an organism.

construct An engineered chimeric DNA designed to be transferred into a cell or tissue. Typically, the construct comprises the gene or genes of interest, a marker gene and appropriate control sequences as a single package. A repeatedly-used construct may be called a cassette.

contained use See: containment.

containment Measures and protocols applied to limit contact of genetically modified organisms or pathogens with the external environment. Synonym: contained use.

contaminant 1. An undesired chemical present in a compound or mixture of compounds. 2. Any micro-organism accidentally introduced into a culture or culture medium. The contaminant may compete with the desired cells and consequently inhibit their growth, or totally replace them.

contig A set of overlapping cloned DNA fragments that can be assembled to represent a defined region of the chromosome or genome from which they were obtained. Contig definition is a necessary step for assembling whole genome sequences.

continuous culture A suspension culture continuously supplied with nutrients by the inflow of fresh medium. The culture volume is normally constant.

continuous fermentation A process in which cells or micro-organisms are maintained in culture in the exponential growth phase by the continuous addition of fresh medium that is exactly balanced by the removal of cell suspension from the bioreactor.

continuous variation Variation where individuals cannot be classified as belonging to one of a set of discrete classes. Characters showing continuous variation are referred to as quantitative. See: polygene, quantitative trait locus. Opposite: discontinuous variation.

controlled environment A closed environment in which parameters, such as light, temperature, relative humidity and sometimes the partial gas pressure (and possibly its composition), are fully controlled.

controlling element In eukaryotes, transposons which affect the activity of known genes. This can occur as a result of the integration within, or close to a gene, thereby disrupting its activity; or following its excision from such a site, thereby restoring activity.

Convention on Biological Diversity (Abbreviation: CBD). The inteRNAtional treaty governing the conservation and use of biological resources around the world, that has also called for the establishment of rules to govern the inteRNAtional movement of non-indigenous living organisms and genetically modified organisms.

conversion The development of a somatic embryo into a plant.

coordinate repression Correlated regulation of a structural gene within an operon by a molecule that interacts with the operator.

copy DNA See: complementary DNA.

copy number The number of a particular plasmid per bacterium cell, or gene per genome.

co-repressor An effector molecule that forms a complex with a repressor and turns off the expression of a gene or set of genes.

corpus A part of the apical meristem below the tunica. In the corpus, cells divide in all directions, and increase in volume.

correlation A statistical association between variables.

cortex Primary tissue of a stem or root, bounded externally by the epidermis and internally in the stem by the phloem, and in the root by the pericycle.

cos ends The 12-base, single-strand, complementary extensions of bacteriophage lambda DNA.

cos sites See cos ends.

co-segregation The joint inheritance of two characters, usually the result of genetic linkage.

cosmid A synthetic plasmid which incorporates the cos ends, and one or more selectable markers such as an antibiotic resistance gene. Cosmids were designed as vectors able to incorporate DNA fragments up to 40-50 kb in size.

co-suppression A natural gene silencing phenomenon, which probably evolved as part of plants' defence against viral attack, but which has become important in the context of plant transgenesis. Operates by inhibiting the expression of transgenes with homology to native DNA through the interaction of native and transgenic mRNA.

cot curve A method to estimate the heterogeneity of sequence of a DNA preparation, based on the observation that the more homogenous the DNA, the more easily (and therefore faster) the annealing of single-stranded DNA will occur. The Cot curve plots the extent of annealing from a fully single-stranded preparation over time. The cot (product of initial concentration and time) at which half the DNA has re-natured is the half-cot, a parameter indicating both the degree of heterogeneity in a complex mixture, and of the extent of complementarity in a mixture of two single-stranded DNA molecules.

co-transfection The procedure by which a baculovirus and a transfer vector are simultaneously introduced into insect cells in culture.

co-transformation A protocol for producing transgenesis, in which host (plant or animal) cells are transformed simultaneously with two different plasmids, one of which carries a selectable marker, and the other the gene to be transferred. Relies on the observation that given a sufficiently high concentration of both plasmids, transformed cells will have incorporated both plasmids, possibly at different genomic loci. If the transgenes are separable through normal meiotic recombination, transgenic individuals without the selectable marker can be selected in subsequent generations.

cotyledon Leaf-like structures at the first node of the seedling stem. In some dicotyledons, they represent a food storage organ for the germinating seedling.

coupling The phase state in which either two dominant or two recessive alleles of two different genes occur on the same chromosome. Synonym: cis configuration. Opposite: repulsion; trans configuration.

covalently-closed circular DNA (Abbreviation: ccc DNA). A DNA molecule in which the free ends have ligated to form a circle. The strands remain linked together even after denaturation. Plasmids exist in this form in their in vivo state. In its native form, ccc DNA will adopt a supercoiled configuration. See: circularization.

CP4 EPSPS Abbreviation for CP4 5-enolpyruvyl-shikimate-3-phosphate synthase. See: enolpyruvyl-shikimate-3-phosphate synthase.

cpDNA Abbreviation for chloroplast DNA.

cross The mating of two individuals or populations. See: cross-breeding.

cross hybridization The annealing of a single-stranded DNA sequence to a single-stranded target DNA to which it is only partially complementary. Often, this refers to the use of a DNA probe to detect homologous sequences in species other than the origin of the probe.

cross pollination Application of pollen from one plant to another to effect the latter's fertilization.

cross pollination efficiency The ease with which cross pollination can be achieved. Generally measured by the number of hybrid progeny generated per flower pollinated.

cross-breeding Mating between members of different populations (lines, breeds, races or species). See: cross.

crossing over The process by which homologous chromosomes exchange material at meiosis through the breakage and reunion of non-sister chromatids. See: recombination, chiasma.

crossing-over unit See: recombination fraction.

cross-over See: chiasma.

crown The base of the stem of cereals and forage species from which tillers or branches arise. In woody plants, the root-stem junction. In forestry, the top portion of the tree.

crown gall A tumorous growth at the base of certain plants characteristic of infection by Agrobacterium tumefaciens. The gall is induced by the transformation of the plant cell by portions of the Ti plasmid.

CRP Abbreviation for catabolite regulator protein. See: catabolite activator protein.

cry proteins A class of crystalline proteins produced by strains of Bacillus thuringiensis, and engineered into crop plants to give resistance against insect pests. These proteins are toxic to certain categories of insects (e.g. corn borers, corn rootworms, mosquitoes, black flies, armyworms, tobacco hornworms, some types of beetles, etc.), but are harmless to mammals and most beneficial insects. Synonym: delta endotoxins.

cryobiological preservation The preservation of germplasm resources in a dormant state by storage at ultra-low temperatures, often in liquid nitrogen. Currently applied to storage of plant seeds and pollen, micro-organisms, animal sperm, and tissue culture cell lines. Synonyms: cryopreservation, freeze preservation.

cryogenic At very low temperature.

cryopreservation See: cryobiological preservation.

cryoprotectant Compound preventing cell damage during successive freezing and thawing processes. Cryoprotectants are agents with high water solubility and low toxicity. Two types commonly used: permeating (glycerol and DMSO) and non-permeating (sugars, dextran, ethylene glycol, polyvinylpyrrolidone and hydroxyethyl starch).

cryptic Anything hidden. 1. Structurally heterozygous individuals that are not identifiable as they do not show abnormal meiotic chromosome pairing configurations ('cryptic structural hybrids'). 2. A form of polymorphism controlled by recessive genes ('cryptic polymorphism'). 3. Any mutation which is exposed by a sensitizing mutation and otherwise poorly detected (such mutations probably escape detection because of the plasticity of composition of the corresponding polypeptide). 4. Phenotypically very similar species (cryptic species) which do not hybridize under normal conditions. 5. Cryptic genetic variation refers to the existence of, for example, alleles conferring high performance for a trait, in a breed that has low performance for that trait.

CTP Abbreviation for 1. cytidine 5'-triphosphate, which is required for RNA synthesis since it is a direct precursor molecule; 2. Chloroplast transit peptide.

cultigen A cultivated plant species with no known wild progenitor.

cultivar (Abbreviation: cv). An inteRNAtionally accepted term denoting a variety of a cultivated plant. Must be distinguishable from other varieties by stated characteristics and must retain their distinguishing characters when reproduced under specific conditions.

culture A population of plant or animal cells or micro-organisms grown under controlled conditions.

culture alteration A term used to indicate a persistent change in the properties of a culture's behaviour (e.g. altered morphology, chromosome constitution, virus susceptibility, nutritional requirements, proliferative capacity, etc.). The term should always be qualified by a precise description of the change which has occurred in the culture.

culture medium Any nutrient system for the cultivation of cells, bacteria or other organisms; usually a complex mixture of organic and inorganic nutrients.

culture room A dedicated room for maintaining cultures, often in a controlled environment.

curing The elimination of a plasmid from its host cell. Many agents which interfere with DNA replication, e.g. ethidium bromide, can cure plasmids from either bacterial or eukaryotic cells.

cut See: cleave.

cuticle Layer of cutin or wax, formed on the outer surface of leaves and fruits, thought to have evolved to reduce evaporative water loss.

cutting A detached plant part that, with appropriate treatment, can regenerate into a complete plant.

cybrid A hybrid, originating from the fusion of a cytoplast (the cytoplasm without nucleus) with a whole cell derived from a different species.

cyclic adenosine monophosphate (Abbreviations: cyclic AMP, cAMP). A "messenger" molecule that regulates many intracellular reactions by transducing signals from extracellular growth factors to cellular metabolic pathways.

cyclic AMP Abbreviation for cyclic adenosine monophosphate.

cyclodextrin Cyclic oligomer of glucose.

cycloheximide A molecule that inhibits protein synthesis in eukaryotes, but not in prokaryotes. It blocks peptide bond formation by binding to the large ribosomal subunits. Synonym: actidione.

cytidine The (ribo)nucleoside resulting from the combination of the base cytosine (C) and the sugar D-ribose. The corresponding deoxyribonucleoside is called deoxycytidine. See: CTP (1), dCTP, cytidylic acid.

cytidine triphosphate (cytidine 5'-triphosphate) See: CTP (1).

cytidylic acid Synonym for cytidine monophosphate (abbreviation: CMP), a (ribo)nucleotide containing the nucleoside cytidine. The corresponding deoxyribonucleotide is called deoxycytidine 5'-monophosphate or deoxycytidylic acid.

cytochrome A class of pigments in plant and animal cells, usually in the mitochondria. They function as electron carriers in respiration.

cytochrome p450 A highly diversified set (more than 1500 known sequences) of heme-containing proteins. Frequently called hydroxylases, although P450 proteins can perform a wide spectrum of other reactions. In bacteria they are soluble and approximately 400 amino acids long; eukaryotic P450s are larger - about 500 amino acids. In mammals they are critical for drug metabolism, haemostasis, cholesterol biosynthesis and steroidogenesis; in plants they are involved in plant hormone synthesis, phytoalexin synthesis, flower petal pigment biosynthesis and many unknown functions. In fungi they make ergosterol and they are involved in pathogenesis. Bacterial P450s are key elements in antibiotic synthesis.

cytogenetics The biology of chromosomes and their relation to the transmission and recombination of genes.

cytokine A generic name for a diverse group of soluble proteins and peptides which act as humoral regulators at extremely small concentrations and which, either under normal or pathological conditions, modulate the functional activities of individual cells and tissues. See: lymphokine, monokine.

cytokinesis Cytoplasmic division and other changes exclusive of nuclear division that are a part of mitosis or meiosis.

cytokinin Plant growth regulators characterized as substances that induce cell division and cell differentiation. In tissue culture, these substances are associated with enhanced callus and shoot development. The compounds are derivatives of adenine. See: kinin.

cytology The study of the structure and function of cells.

cytolysis Cell disintegration.

cytoplasm The living material of the cell, exclusive of the nucleus, consisting of a complex protein matrix or gel, and where essential membranes and cellular organelles (mitochondria, plastids, etc.) reside.

cytoplasmic genes Genes located on DNA outside the nucleus, i.e. on plastids.

cytoplasmic inheritance Hereditary transmission dependent on cytoplasmic genes.

cytoplasmic male sterility Genetic defect due to faulty functioning of mitochondria in pollen development, preventing the formation of viable pollen. Commonly found or inducible in many plant species and exploited for some F₁ hybrid seed programmes.

cytoplasmic organelles Discrete sub-cellular structures located in the cytoplasm of cells - mitochondria, plastids and lysosomes.

cytosine (Abbreviation: C). One the bases found in DNA and RNA. See: cytidine.

cytosol The fluid portion of the cytoplasm, i.e. the cytoplasm minus its organelles.

cytotoxic T cell See: killer T cell.

cytotoxicity Poisoning of the cell.

cytotype A maternally inherited cellular condition in Drosophila that regulates the activity of transposable P elements.