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- A -

A  Adenine residue, in either DNA or RNA.

Ab  See antibody.

abiotic stress  The effect of non-living factors which can harm living organisms. These non-living factors include drought, extreme temperatures, pollutants, etc.

abscisic acid  A plant growth regulator involved in abscission, dormancy, stomatal opening/closure, and inhibition of seed germination. It also affects the regulation of somatic cell embryogenesis in some plant species.

absciss; abscissa  The horizontal axis of a graph. cf ordinate.

absorb (L. ab, away + sorbere, to suck in)  To suck up, or to take in. In the cell, materials are taken in (absorbed) from a solution. cf adsorb.

absorption  In general: the process of absorbing; taking up of water and nutrients by assimilation or imbibition. The taking up by capillary, osmotic, chemical or solvent action, such as the taking up of a gas by a solid or liquid, or taking up of a liquid by a solid. cf adsorption.

abzyme  See catalytic antibody.

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

accessory bud  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 (q.v.). cf acquired.

acellular  Describing tissues or organisms that are not made up of separate cells but often have more than one nucleus. cf syncytium.

acentric chromosome  Chromosome fragment lacking a centromere.

acetyl co-enzyme A; 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.

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  1. Developing or blooming in succession towards the apex, such as leaves or flowers developing acropetally.

acrosome  An apical organelle in the head of a spermatozoon, q.v.

acrylamide gels  See polyacrylamide gels.

actin  One of the two contractile proteins in muscle (the other being myosin). Actin is also found in the microfilaments that form part of the cytoskeleton of all cells.

activated charcoal; activated carbon  Charcoal which 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. Rooting factors such as phenolamines present as contaminants in charcoal may stimulate growth in vitro. Its addition to rooting medium may stimulate root initiation in some plant species. Activated charcoal may differ in origin and in composition. cf charcoal; phenolic oxidation.

active collection  In PGR: Defined in the International Undertaking on Plant Genetic Resources (FAO, 1983) as a collection which complements a base collection (q.v.) and is a collection from which seed samples are drawn for distribution, exchange and other purposes such as multiplication and evaluation.

activator  1. A substance or physical agent that stimulates transcription of a specific gene or operon.

active site  1. A site on the surface of a catalyst at which activity occurs.

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

adaptation traits  In AnGR: The complex of traits related to reproduction and survival of the individual in a particular production environment. Adaptation traits contribute to individual fitness; they are the traits subjected to selection during the evolution of animal genetic resources. By definition, these traits are also important to the ability of the animal genetic resource to be sustained in the production environment. (Based on FAO, 1999)

adaptive radiation  The evolution of new forms, sub-species or species from one species of plant or animal in order to exploit new habitats or food sources. a.k.a. divergent evolution.

adaptor  1. A synthetic double-stranded oligonucleotide that has a blunt end, while the other end has a nucleotide extension that can base pair with a cohesive end created by cleavage of a DNA molecule with a specific type II restriction endonuclease. The blunt end of the adaptor can be ligated to the ends of a target DNA molecule and the construct can be cloned into a vector by using the cohesive ends of the adaptor.

addendum (pl: addenda)  In formulation of tissue culture media: an item or a constituent substance to be added.

additive allelic effects  Effects of alleles at a locus, where the heterozygote is exactly intermediate between the two homozygotes.

additive gene effects  Additive allelic effects summed across all the loci that contribute to genetic variation in a quantitative trait.

adenilate cyclase  The enzyme that catalyses the formation of cyclic AMP.

adenine (C5H5N5; f.w. 135.14) (symbol: A)  A white crystalline purine base. A constituent of DNA and RNA and nucleotides such as ADP and ATP. A B-group vitamin (B4) generally available as C5H5N5.3H2O, m.w. 189.13. It is added to some tissue culture media, as adenine sulphate, to promote shoot formation and for its weak cytokinin effect. It is present in plant tissues combined with aminoamide, phosphoric acids and D-ribose.

adenosine disphosphate (ADP)  See ATP.

adenosine monophosphate (AMP)  See ATP.

adenosine triphospate (ATP)  See ATP.

adenovirus  A group of DNA viruses which cause diseases in animals. In man, they produce acute respiratory tract infections with symptoms resembling common cold. They are used in gene cloning, as vectors for expressing large amounts of recombinant proteins in animal cells. They are also used to make live-virus vaccines against more dangerous pathogens. See viral vaccines.

ADEPT (antibody-directed enzyme pro-drug therapy)  A way to target a drug to a specific tissue. The drug is administered as an inactive pro-drug, and then converted into an active drug by an enzyme administered with a second injection. The enzyme is coupled to an antibody that concentrates it in the target tissue. When the enzyme arrives at the target tissue, the pro-drug is activated to form the active drug, while elsewhere it remains inactive. See drug delivery; targeted drug delivery.

adhesion (L. adhaerere, to stick to)  The attraction of dissimilar molecules for each other. A sticking together of unlike substances, such as soil and water.

A-DNA  A right-handed DNA double helix that has 11 base pairs per turn. DNA exists in this form when partially dehydrated.

ADP (adenosine diphosphate)  See ATP.

adsorb  See adsorption.

adsorbent  Noun: A substance to which compounds adhere. In tissue culture, an adsorbent is added to the culture medium to adsorb compounds released by cultured cells or tissues, thus minimizing any adverse effect on the subsequent growth in culture. A common adsorbent in tissue culture is activated charcoal, q.v.

adsorption  The formation of a layer of gas, liquid or solid on the surface of a solid. cf absorption.

adult cloning The creation of identical copies of an adult animal by nuclear transfer (q.v.) from differentiated adult tissue. See also cloning; Dolly.

advanced  Applied to an organism or a part thereof, implying considerable development from the ancestral stage or from the explant stage.

adventitious (L. adventitius, not properly belonging to)  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.

aerate  To supply with or mix with air or gas. The process is aeration.

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

aerobic bacteria  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.

aerobic  Active in the presence of free oxygen.

affinity chromatography  A method for separating molecules by exploiting their ability to bind specifically to other molecules. There are several types of biological affinity chromatography. A biological molecule can be immobilized and a smaller molecule (ligand, q.v.,) to which it is to bind can be stuck to it, or the smaller ligand can be immobilized and the macromolecule stuck to it. A variant is to use an antibody as the immobilized molecule and use it to "capture" its antigen: this is often called immuno-affinity chromatography. A variation is pseudo-affinity chromatography, in which a compound which is like a biological ligand is immobilized on a solid material, and enzymes or other proteins are bound to it. Other techniques include metal affinity chromatography, where a metal ion is immobilized on a solid support: metal ions bind tightly and specifically to many biomolecules. The metal ion is bound to a chelator or chelating group, a chemical group that binds specifically and extremely tightly to that metal.

affinity tag; purification tag  An amino acid sequence that has been engineered into a protein to make its purification easier. These can work in a number of ways. The tag could be another protein, which binds to some other material very tightly and thus allowing the protein to be purified by affinity chromatography (q.v.). The tag could be a short amino acid sequence, which is recognized by an antibody. The antibody would then bind to the protein whereas it would not have done so before. One such short peptide, called FLAG, has been designed so that it is particularly easy to make antibodies against it. The tag could be a few amino acids, which are then used as a chemical tag on the protein. For example, a string of positively charged amino acids will bind very strongly to a negatively charged filter: this could be used as the basis of a separation system. Some amino acids bind metals very strongly, especially in pairs: this chemical property can be exploited by using a filter with metal atoms chemically linked onto it to pull a protein out of a mixture of proteins. cf affinity chromatography.

aflatoxin  Toxic compounds, produced by moulds (fungi) of the Aspergillus flavus group, that bind to DNA and prevent replication and transcription. Aflatoxins can cause acute liver damage and cancer. Animals may be poisoned by eating stored food or feed contaminated with the mould.

AFLP  See amplified fragment length polymorphism.

Ag  See antigen.

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

agarose  The main constituent of agar.

agarose gel electrophoresis  A process in which a matrix composed of a highly purified form of agar is used to separate larger DNA and RNA molecules. See electrophoresis.

aggregate  1. A clump or mass formed by gathering or collecting units.

agonist  A drug, hormone or transmitter substance that forms a complex with a receptor site that is capable of triggering an active response from a cell.

agricultural biological diversity  See agrobiodiversity.

Agrobacterium  A genus of bacteria that includes several plant pathogenic species, causing tumour-like symptoms. See Agrobacterium tumefaciens; crown gall; hairy root culture; Ri plasmid; Ti plasmid.

Agrobacterium tumefaciens  A bacterium that causes crown gall disease in some plants. The bacterium infects a wound, and injects a short stretch of DNA into some of the cells around the wound. The DNA comes from a large plasmid - the Ti (tumour induction) plasmid - a short region of which (called T-DNA, = transferred DNA) is transferred to the plant cell, where it causes the cell to grow into a tumour-like structure. The T-DNA contains genes which inter alia allows the infected plant cells to make two unusual compounds, nopaline and octopine, that are characteristic of transformed cells. The cells form a gall, which hosts the bacterium. This DNA-transfer mechanism is exploited in the genetic engineering of plants. The Ti plasmid is modified so that a foreign gene is transferred into the plant cell along with or instead of the nopaline synthesis genes. When the bacterium is cultured with isolated plant cells or with wounded plant tissues, the "new" gene is injected into the cells and ends up integrated into the chromosomes of the plant.

Agrobacterium tumefaciens-mediated transformation  A naturally occurring process of DNA transfer from the bacterium A. tumefaciens to plants.

agrobiodiversity; agricultural biological diversity  That component of biodiversity that is relevant to food and agriculture production. The term agrobiodiversity encompasses within-species, species and ecosystem diversity. (Based on FAO, 1999)

AI  See artificial insemination.

AIDS (acquired immunodeficiency syndrome)  The usually fatal human disease in which the immune system is destroyed by a retrovirus (Human Immunodeficiency Virus, HIV). The virus infects and destroys helper T-cells, which are essential for combating infections.

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. The term is also used for absence of chlorophyll in plants.

albino  1. An organism lacking pigmentation, due to genetic factors. The condition is albinism, q.v.

aleurone  The outermost layer of the endosperm in a seed.

algal biomass  Single-celled plants, such as Chlorella spp. and Spirulina spp., are grown commercially in ponds to make feed materials. Chlorella is grown commercially to make into fish food: it is fed to zooplankton, and these in turn are harvested as feed for fish farms. This is a means of converting sunlight into food in a way more convenient and controllable than normal farming.

alginate  Polysaccharide gelling agent.

alkylating agents  Chemicals that transfer alkyl (methyl, ethyl, etc.) groups to the bases in DNA.

allele (Gr. allelon, of one another, mutually each other); allelomorph (adj: allelic, allelomorphic). One of a pair, or series, of variant forms of a gene that occur at a given locus in a chromosome. Alleles are symbolized with the same basic symbol (e.g., B for dominant and b for recessive); B1, B2, ..., Bn for n additive alleles at a locus). In a normal diploid cell there are two alleles of any one gene (one from each parent), which occupy the same relative position (locus) on homologous chromosomes. Within a population there may be more than two alleles of a gene. See multiple alleles.

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

allele-specific amplification (ASA) The use of polymerase chain reaction (PCR) at a sufficiently high stringency that only a primer with exactly the same sequence as the target DNA will be 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. The "allele" on the other homologous chromosome in a diploid mammalian cell cannot undergo a functional re-arrangement, which would result in the production of two different antibodies by a single plasma cell.

allelomorph  See allele.

allelopathy  The phenomenon by which the secretion of chemicals, such as phenolic and terpenoid compounds, by a plant inhibits the growth or reproduction of other plant species with which it is competing.

allergen  An antigen that provokes an immune response.

allogamy  Cross fertilization in plants. See fertilization.

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

allopolyploid (Gr. allos, other, + polyploidy). A polyploid organism (usually a plant) having multiple sets of chromosomes derived from different species. Hybrids are usually sterile, because they do not have sets of homologous chromosomes and therefore pairing cannot take place. However, if doubling of the chromosome number occurs in a hybrid derived from two diploid (2n) species, the resulting tetraploid (4n) is a fertile plant, since it contains two sets of homologous chromosome and pairing may occur; this tetraploid is an allotetraploid.

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 of allosteric enzymes 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.

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

allotetraploid  An organism with four genomes derived from hybridization of different species. Usually, in forms that become established, two of the four genomes are from one species and two are from another species. See allopolyploid.

allozygote  A diploid individual that is homozygous at a locus in which the two genes are not identical by descent from a common ancestor.

allozyme  See allosteric enzyme.

alphalactalbumin  Protein component of milk.

alternative mRNA splicing  The inclusion or exclusion of different exons to form different mRNA transcripts. See RNA.

Alu sequences  A family of 300-bp sequences occurring nearly a million times in the human genome.

ambient temperature  Air temperature at a given time and place; not radiant temperature.

amino acid (Gr. Ammon, from the Egyptian sun god, in M. L. used in connection with ammonium salts). An acid containing the group NH2. In particular, any of 20 basic building blocks of proteins with a free amino (NH2) and a free carboxyl (COOH) group, and having the basic formula NH2 - CR - COOH. According to the side group R, they are subdivided into: polar or hydrophilic (serine, threonine, tyrosine, asparagine and glutamine); non-polar or hydrophobic (glycine, alanine, valine, leucine, isoleucine, proline, phenylalanine, tryptophan and cysteine); acidic (aspartic acid and glutamic acid) and basics (lysine, arginine, hystidine). The sequence of amino acids determines the shape, properties and the biological role of a protein. Plants and many micro-organisms can synthesize amino acids from simple inorganic compounds, but animals are unable to synthesize some of them, called essential amino acids, so they must be present in the diet.

aminoacyl site; A-site  One of two sites on ribosomes to which the incoming aminoacyl tRNA binds.

aminoacyl tRNA synthetase  Enzyme that attaches each amino acid to its specific tRNA molecule.

amitosis  Cell division (cytokinesis), including nuclear division through constriction of the nucleus, without chromosome differentiation as in mitosis. The maintenance of genetic integrity and diploidy during amitosis is uncertain. This process occurs in the endosperm of flowering plants.

amniocentesis  A procedure for obtaining amniotic fluid from a pregnant mammal for the diagnosis of some diseases in the unborn foetus. Cells are cultured, and metaphase chromosomes are examined for irregularities (e.g., Down syndrome, spina bifida, etc., 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 cells of the embryo (not of the mother). Both fluid and cells are used for diagnosis of genetic abnormalities in the embryo or foetus.

amorph; null mutation  A mutation that obliterates gene function.

AMP (adenosine monophosphate)  See ATP.

amphidiploid  A species or type of plant derived from doubling the chromosomes in the F1 hybrid of two species; an allopolyploid. In an amphidiploid the two species are known, whereas in other allopolyploids they may not be known.

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

ampicillin (b-lactamase)  A penicillin-derived antibiotic that prevents bacterial growth by interfering with synthesis of the cell wall.

amplification  1. Treatment (e.g., use of chloramphenicol) designed to increase the proportion of plasmid DNA relative to that of bacterial (host) DNA.

amplified fragment length polymorphism (AFLP)  A type of DNA marker, generated by digestion of genomic DNA with two restriction enzymes to create many DNA fragments, ligation of specific sequences of DNA (called adaptors) to the ends of these fragments, amplification of the fragments via PCR (using a set of primers with sequences corresponding to the adapters, plus various random combinations of three additional bases at the end), and visualization of fragments via gel electrophoresis. The PCR will amplify any fragment whose sequence happens to start with any of the three-base sequences in the set of primers. AFLPs have the important advantage that many markers can be generated with relatively little effort. They are a very useful means of quantifying the extent of genetic diversity within and between populations. Their major disadvantage is that they are not specific to a particular locus and, because they are scored as the presence or absence of a band, heterozygotes cannot be distinguished from homozygotes, i.e., they are inherited in a dominant fashion.

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 (PCR).

ampometric  See enzyme electrode.

amylase  A group of enzymes that degrade starch, glycogen and other polysaccharides, producing a mixture of glucose and maltose. Plants have both a- and b-amylase; animal have only a-amylase.

amylolytic  The capability of breaking down starch into sugars.

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

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

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

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, such as alcoholic fermentation, in which one of the end products is 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 (Gr. ana, up + phais, appearance)  The stage of mitosis or meiosis during which the daughter chromosomes (sister chromatids) pass from the equatorial plate 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.

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 by the testes.

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. Androgenesis is detected by cytological staining. See anther culture; gynogenesis; parthenogenesis.

aneuploid  (Gr. aneu, without + ploid)  An organism or cell having a chromosome number that is not an exact multiple of the monoploid (x) with one chromosome being present in greater (e.g., trisomic 2n + 1) or lesser (e.g., monosomic 2n - 1) number than the normal diploid number.

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. Typical materials are hollow fibre membrane bioreactors, or porous carriers made of polysaccharide, protein, plastic or ceramic materials with microscopic holes inside which the cells grow.

animal cloning See cloning.

animal genetic resources databank  A databank that contains inventories of farm animal genetic resources and their immediate wild relatives, including any information that helps to characterize these resources. (Source: FAO, 1999)

animal genome (gene) bank  A planned and managed repository containing animal genetic resources. Repositories include the environment in which the genetic resource has developed, or is now normally found (in situ) or facilities elsewhere (ex situ - in vivo or in vitro). For in vitro, ex situ genome bank facilities, germplasm is stored in the form of one or more of the following: semen, ova, embryos and tissue samples. (Source: FAO, 1999)

anion  A negatively charged ion; opposite: cation.

anneal  The pairing of complementary DNA or RNA sequences, via hydrogen bonding, to form a double-stranded polynucleotide. Most often used to describe the binding of a short primer or probe.

annealing  The process of heating (de-naturing step) and slowly cooling (re-naturing step) double-stranded DNA to allow the formation of hybrid DNA or complementary strands of DNA or of DNA and RNA.

annual (L. annualis, within a year)  1. (adj:) Taking one year, or occurring at intervals of one year.

anonymous DNA marker  A DNA marker (q.v.) detectable by virtue of variation in its sequence, irrespective of whether or not it actually occurs in or near a coding sequence. Microsatellites 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. cf 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 culture  The aseptic culture of anthers for the production of haploid plants from microspores. See androgenesis; gynogenesis; parthenogenesis.

anther  Microsporangium bearing microspores which develop into pollen (microgametophytes). The upper part of a stamen, containing pollen sacs within which are numerous pollen grains.

anthesis  The flowering period or efflorescence. Anthesis is the time of full bloom, which lasts till fruit set.

anthocyanin  Water-soluble blue, purple and red flavonoid pigments found in vacuoles of cells.

antiauxin  A chemical that interferes with the auxin response. Antiauxin may or may not involve prevention of auxin transport or movement in plants. Some antiauxins are said to promote morphogenesis in vitro, such as 2,3,5-tri-iodobenzoate (TIBA; f.w. 499.81), or 2,4,5-trichlorophenoxyacetate (2,4,5-T; m.w. 255.49), which 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 such as penicillin are often used to control (to some extent kill) contaminating organisms. However, resistance to particular antibiotics can be acquired through mutations. Some contaminating organisms are only suppressed or their metabolism slowed to an insignificant level. See antibiotic resistance; bactericide; bacteriostat.

antibiotic resistance  The ability of a micro-organism to produce a protein that disables an antibiotic or prevents transport of the antibiotic into the cell.

antibody (Gr. anti, against + body)  An immunological protein (called an immunoglobulin, Ig) produced by certain white blood cells (lymphocytes) of the immune system of an organism in response to a contact with a foreign substance (antigen). Such an immunological protein has the ability of specifically binding with the foreign substance and rendering it harmless. The basic immunoglobulin molecule consists of two identical heavy and two identical light chains. See monoclonal antibodies; polyclonal antibodies.

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  Antibodies have a well-defined structure. Each antibody has two identical "light" chains and two identical "heavy" chains. Each chain comprises a constant region, i.e., a region that is the same between antibodies of the same class and sub-class, and a variable region that differs between. The antigen-binding region or binding site - complementarity determining region - is in the variable region. The antibody can be cut by proteases into several fragments, known as Fab, Fab', and Fc.

antibody-mediated (humoral) immune response  The synthesis of antibodies by B cells in response to an encounter of the cells of the immune system with a foreign immunogen.

anticlinal  The plane of cell wall orientation or cell division perpendicular (at right angles) to the surface of an organ. See tunica; periclinal.

anticoding strand  The strand of the DNA double helix that is actually transcribed. Also known as the antisense or template strand.

anticodon  A triplet of nucleotides in a tRNA molecule that pairs with a complementary triplet of nucleotides, or codon, in an mRNA molecule during translation. See codon; mRNA; RNA; tRNA.

antigen; immunogen  A compound that elicits an immune response by stimulating the production of antibodies. The antigen, usually a protein, when introduced into a vertebrate organism is bound by the antibody or a T cell receptor. See antigenic determinant; antigenic switching.

antigenic determinant  A surface feature of a micro-organism or macromolecule, such as a glycoprotein, that elicits an immune response. See 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 globulin  Blood globulin that reduces the clotting time of haemophilic blood.

anti-idiotype antibodies  Antibodies which recognize the binding sites of other antibodies. Their binding sites are complementary to the binding sites of another immunoglobulin. When an animal becomes immune to something, it not only acquires antibodies against that something, it also acquires antibodies against those antibodies. This forms a network of antibodies which can all bind to each other to various degrees, helping to regulate 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 harms the growth of micro-organisms.

antinutrients  Compounds that inhibit normal uptake of nutrients.

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

antioxidant solution  Pre-treatment solution (e.g., Vitamin C; citric acid) that retards senescence and browning of tissue. It is employed to incubate explants prior to surface sterilization.

antioxidant  Compound that slows the rate of oxidation reactions.

antiparallel orientation  The normal arrangement of the two strands of a 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  1. The strand of chromosomal DNA that is transcribed.

antisense gene  A gene that produces a transcript (mRNA) that is complementary to the pre-mRNA or mRNA 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. See RNA.

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 animal (after coagulation of the blood), containing antibodies

anti-terminator  A type of protein which enables RNA polymerase to ignore certain transcriptional stop or termination signals and read through them to produce longer mRNA transcripts.

antitranspirant  A compound designed to reduce transpiration when sprayed or painted on leaves of newly transplanted trees, shrubs or vines, or used as a dip for cuttings in lieu of misting; may interfere with photosynthesis and respiration if the coating is too thick or unbroken.

apex (L. apex, a tip, point, or extremity; pl: apices)  The tip, point or angular summit. The tip of a leaf; the portion of a root or shoot containing apical and primary meristems. Usually used to designate the apical tip of the meristem.

apical cell  A meristematic initial in the apical meristem of shoots or roots of plants. As this cell divides, new tissues are formed.

apical dominance  The phenomenon of inhibition of growth of lateral (axillary) buds in a plant by the presence of the terminal (apical) bud on the branch, due to auxins produced by 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: (i) An outer 1-4-cell layered region (called the tunica), where cell divisions are anticlinal, i.e., perpendicular to the surface; and below the tunica, (ii) the corpus, where the cells divide in all directions, giving them an increase in volume.

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

apomixis (Gr. apo, away from + mixis, a mingling; adj: apomictic) The asexual production of diploid offspring without the fusion of gametes. The embryo develops by mitotic division of the maternal or paternal gamete, or, in the case of plants, by mitotic division of a diploid cell of the ovule.
androgenesis; gynogenesis; panmixis; parthenogenesis.

apoptosis  The process of cell death, which occurs naturally as a part of normal development, maintenance and renewal of tissue in an organism. Apoptosis differs from necrosis, in which cell death is caused by a toxic substance.

aquaculture  Growing of water plants and animals, rather than harvesting them from wherever they happen to grow in rivers or seas. Usually aquaculture uses fresh water; when it uses sea water it can be called mariculture. It is considered to be a part of biotechnology (although peripheral) because it is a new commercial development, and because it often involves growing organisms in large volumes of water, which has similarities to growing large volumes of yeast or bacteria. Biotechnology also provides clean, well-aerated water for the animals to grow in; food, such as krill or powdered synthetic food; and food additives, such as astaxanthins to ensure that fish and prawns have the right colour. Aquaculture has also been used to mass-produce macro- and micro-algae for chemicals, vitamins and pigments. For both animals and plants, biotechnologists have been using genetic methods to produce triploid and tetraploid organisms, and hybrid algae through plant cell fusions. Triploid trout, for example, are sterile, and can be used for biocontrol of weeds without the threat of their being able to breed themselves.

Arabidopsis  A genus of flowering plants in the Cruciferae. A. thaliana is used in research as a model plant because it has a small genome (5 pairs of chromosomes; 2n = 10) and can be cultured easily, with a generation time of two months.

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

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

artificial insemination  The deposition of semen, using a syringe, at the mouth of the uterus to make conception possible. It is used in the breeding of domestic animals.

artificial medium  See culture medium.

artificial seed  Encapsulated or coated somatic embryos (embryoids) 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 See allele-specific amplification.

ascorbic acid; vitamin C (C6H8O6; f.w. 176.12)  A water-soluble vitamin present naturally in some plants, and also synthetically produced. Aside from its role as a vitamin, it is used as an antioxidant in plant tissue culture; and included in disinfection solutions.

ascospore  One of the spores contained in the ascus (q.v.) of certain fungi.

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

aseptic  Asepsis or sterile. The state of being free of contaminating organisms (bacteria, fungi, algae and all micro-organisms except viruses) but not necessarily free of internal symbionts. See axenic.

asexual (Gr. a, without + L. sexualis, sexual)  Any type of reproduction not involving meiosis or the union of gametes.

asexual embryogenesis  The sequence of events whereby embryos develop from somatic cells. a.k.a. somatic cell embryogenesis.

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

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  See aminoacyl site.

Asn  See asparagine.

asparagine (abbr: Asn; C4H8N2O3; f.w. 132.12)  One of the 20 essential amino acids. It is occasionally included in plant tissue culture media as a source of reduced nitrogen.

aspartic acid (abbr: Asp; C4H7NO4; f.w. 132.12)  An amino acid necessary for nucleotide synthesis and occasionally included in plant tissue culture media.

assay  1. To test or evaluate.

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

assortment  See segregation.

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

ATP (adenosine triphosphate)  A nucleotide of fundamental importance as a carrier of chemical energy in all living organisms. It consists of adenosine with three phosphate groups, linked together linearly. The phosphates are attached to adenosine through its ribose (sugar) portion. Upon hydrolysis, bonds yield either one molecule of ADP (adenosine diphosphate) and an inorganic phosphate, or one molecule of AMP (adenosine monophosphate) and pyrophosphate; in both cases releasing energy that is used to power biological processes. ATP is regenerated by rephosphorilation of AMP and ADP, using chemical energy derived from the oxidation of food.

ATP-ase  An enzyme that brings about the hydrolysis of ATP, by the cleavage of either one phosphate group 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.

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.

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. Usually the catalysis starts slowly and increases as the quantity of the catalyst increases, falling off as the product is used up.

autocatalytic reaction  See autocatalysis.

autoclave  1. An enclosed chamber in which substances are heated under pressure to sterilize utensils, liquids, glassware, etc., using steam. The routine method uses steam pressure of 103.4×103 Pa at 121°C for 15 minutes, or longer to allow large volumes to reach the critical temperature.

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 that are taken from an individual, cultured (or stored), and, possibly, genetically manipulated before being infused back into the original donor.

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

autonomous(ly) replicating segment (or sequence)   See ARS.

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.

autopolyploid  A polyploid that has multiple and identical or nearly identical sets of chromosomes (genomes) all derived from the same species. A polyploid species with genomes derived from the same original species.

autoradiograph A picture prepared by labelling a substance such as DNA with a radioactive material such as tritiated thymidine and allowing the image produced by decay radiation to develop on a film over a period of time.

autoradiography  A technique that captures the image formed in a photographic emulsion as a result of the emission of either light or radioactivity from a labelled component that is placed next to unexposed film. The technique is used for detecting the location of an isotope in a tissue, cell or molecule. The sample is placed in contact with a photographic emulsion, usually an X-ray film. The emission of b-particles from the sample activates the silver halide grains in the emulsion and allows them to reduce to metallic silver when the film is developed. In genetic engineering, autoradiography is most commonly used to detect the hybridization of a radioactive DNA (probe) molecule to denatured DNA in either the Southern transfer or colony hybridization procedures.

autosome  A chromosome that is not involved in sex determination.

autotrophic  Self-nourishing organisms capable of utilizing carbon dioxide or carbonates as the sole source of carbon and obtaining energy for life processes from radiant energy or from the oxidation of inorganic elements, or compounds such as iron, sulphur, hydrogen, ammonium and nitrites. See heterotrophic.

autotrophy  Autotrophy is the capacity of an organism to use light as the sole energy source in the synthesis of organic material from inorganic elements or compounds. Autotrophic organisms include green photosynthesizing plants and some photosynthetic bacteria. cf  heterotrophy.

auxin (Gr. auxein, to increase)  A group of plant growth regulators (natural or synthetic) which stimulate cell division, enlargement, apical dominance, root initiation, and flowering. One naturally produced auxin is indole-acetic acid (IAA).

auxin-cytokinin ratio  The relative proportion of auxin to cytokinin present in plant-tissue-culture media. Varying the relative amounts of these two hormone groups in tissue culture formulae affects the proportional growth of shoots and roots in vitro. As the ratio is increased (increased auxin or decreased cytokinin), roots are more likely to be produced, and as it is decreased root growth declines and shoot initiation and growth are promoted. This relationship was first recognized by C.O. Miller and F. Skoog in the 1950s.

auxotroph (Gr. auxein, to increase + trophe, nourishment)  A mutant cell or micro-organism lacking the capacity to form an enzyme or metabolite present in the parental strain, and that consequently will not grow on a minimal medium, but requires the addition of some compound - such as an amino acid or a vitamin - for growth.

availability  A reflection of the form and location of nutritional elements and their suitability for absorption. In tissue culture media this is related to the abundance of each nutritional element, the osmotic concentration and pH of the medium, the stability and solubility of the item in question, the presence of absorbing agents in the media, and other factors.

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

axillary bud  A bud found at the axil of a leaf (synonymous with lateral bud).

axillary bud proliferation  Propagation in culture using protocols and media which promote axillary (lateral shoot) growth. This is a technique for mass production (micropropagation) of plantlets in culture, achieved primarily through hormonal inhibition of apical dominance and stimulation of lateral branching.

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