BABS (biosynthetic antibody binding sites) See dabs.
BAC (bacterial artificial chromosome) A cloning vector constructed from bacterial fertility (F) factors; like YAC vectors, they accept large inserts of size 200 to 500 kb. See cloning vector; YAC.
bacillus A rod-shaped bacterium.
Bacillus thuringiensis (Bt) A bacterium that kills insects; a major component of the microbial pesticide industry.
back mutation A second mutation at the same site in a gene as the original mutation. The second mutation restores the wild-type nucleotide sequence.
backcross Crossing an organism 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. See testcross.
bacteria Plural of bacterium, q.v.
bacterial toxin A toxin produced by a bacterium, such as Bt toxin by Bacillus thuringiensis.
bacteriocide; bactericide 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 A virus that infects bacteria. Also called simply phage. Altered forms are used in DNA cloning work, where they are convenient vectors. The bacteriophages most used are derived from two "wild" phages, called M13 and lambda (l). Lambda phages are used to clone segments of DNA in the range of around 10-20 kb. They are lytic phages, i.e., they replicate by lysing their host cell and releasing more phages. On a bacteriological plate, this results in a small clear zone - a plaque. Some lambda vectors have also been developed which are expression vectors (q.v.). The M13 system can grow inside a bacterium, so that it does not destroy the cell it infects but causes it to make new phages continuously. It is a single-stranded DNA phage, and is used for the Sanger di-deoxy DNA sequencing method (see DNA sequencing). Both of these phages grow on Escherichia coli as a host bacterium.
bacteriostat A substance that inhibits or slows down growth and reproduction of bacteria.
bacterium (Gr. bakterion, a stick; pl: bacteria) Common name for the class Schizomycetes: minute (0.5-5mm), unicellular organisms, without a distinct nucleus. Bacteria are prokaryotes, and most of them are identified by means of Gram staining (q.v.). They are classified on the basis of their oxygen requirement (aerobic vs anaerobic) and shape (spherical = coccus; rodlike = bacillus; spiral = spirillum; comma-shaped = vibrio; corkscrew-shaped = spirochaete; filamentous). Bacteria usually reproduce asexually, by simple cell division, although a few undergo a form of sexual reproduction, termed conjugation. A few bacteria can photosynthesize (including green-blue cyanobacteria), some are saprophytes and others are parasites and can cause diseases. They are major agents of fermentation, putrefaction and decay, and frequently a source of contamination in tissue culture. In plant pathology, strains of bacteria causing disease in specific plant cultivars are called pathovars (q.v.).
baculovirus Baculoviruses are a class of insect virus which have been used to make DNA cloning vectors for gene expression in eukaryotic cells. Baculoviruses have a gene which is expressed at very high levels late in their infection cycle, filling the nucleus of the cell with many-sided bodies full of a protein which is not needed to produce more viruses, but is necessary for the virus's spread in the wild. In a vector cloning system, this gene is replaced by one that the biotechnologist wants expressed. Production of the 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. Being an animal expression system, baculoviruses produce proteins that are glycosylated (addition of carbohydrates) like the proteins in animals, making it an attractive option for the production of biopharmaceuticals. In addition, baculoviruses are non-infective and non-pathogenic to vertebrates.
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 types of individuals maintained in the same breeding population.
bank See gene bank.
bar A unit used for pressure of fluid. 1 bar = 105 Pa. 1 bar is approximately equivalent to 1 atmosphere.
Barr body A condensed mass of chromatin found in the nuclei of female mammals. It is a late-replicating, inactive X-chromosome. Named after its discoverer, Murray Barr (1908-).
basal 1. Located at the base of a plant or a plant organ.
2. A fundamental formulation of a tissue culture medium.
basal body Small granule to which a cilium or flagellum is attached. cf kinetosome.
base A cyclic, nitrogen-containing compound that is one of the essential components of nucleic acids. Exists in five main forms (adenine, A; guanine, G; thymine, T; cytosine, C; uracil, U). A and G have a similar structure and are called purines; T, C and U have a similar structure and are called pyrimidines. A base joined to a ribose sugar joined to a phosphate group is a nucleotide - the building block of nucleic acids.
base analogues Unnatural purine or pyrimidine bases that differ slightly in structure from the normal bases, but can be incorporated into nucleic acids. They are often mutagenic.
base collection In PGR: Defined in the International Undertaking on Plant Genetic Resources (FAO, 1983) as a collection of seed stock or vegetative propagating material (ranging from tissue cultures to whole plants) held for long-term security in order to preserve the genetic variation for scientific purposes and as a basis for plant breeding as multiplication and evaluation. cf active collection.
base pair (bp) The two strands that constitute DNA are held together by specific hydrogen bonding between purines and pyrimidines (A pairs with T; and G pairs with C). The size of a nucleic acid molecule is often described in terms of the number of base pairs (symbol: bp) or thousand base pairs (kilobase pairs; symbol: kb; a more convenient unit) it contains.
base substitution Replacement of one base by another in a DNA molecule. See transition; transversion.
basipetal See acropetal.
basophil A type of white blood cell (leucocyte), 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. cf continuous culture; batch fermentation.
batch fermentation A process in which cells or micro-organisms are grown for a limited time. At the beginning of the fermentation, an inoculum is introduced into fresh medium, with no addition or removal of medium for the duration of the process.
B cells An important class of white blood cells that mature in bone marrow and produce antibodies. They are largely responsible for the antibody-mediated or humoral immune response; they give rise to the antibody-producing plasma cells and some other cells of the immune system. See B lymphocytes.
b-DNA The normal form of DNA found in biological systems. It exists as a right-handed helix.
bench-scale process A small- or laboratory-scale process; commonly used in connection with fermentation.
beta-DNA See b-DNA.
beta-galactosidase See b-galactosidase.
beta-lactamase See b-lactamase
b-galactosidase An enzyme that catalyses the formation of glucose and galactose from lactose.
biennial (L. biennium, a period of two years) In botany, a plant which completes its life cycle within two years and then dies. For most biennial plants, the two growing seasons have to be separated by a period of cold temperature sufficient to induce flowering and fruit formation.
bifunctional vector See shuttle vector.
binary vector system A two-plasmid system in Agrobacterium tumefaciens for transferring into plant cells a segment of T-DNA that carries cloned genes. One plasmid contains the virulence gene (responsible for transfer of the T-DNA), and another plasmid contains the T-DNA borders, the selectable marker and the DNA to be transferred. See also cDNA; carrier DNA; plasmid; vector.
binding The ability of molecules to stick to each other because of the exact shape and chemical nature of parts of their surfaces. Many biological molecules bind extremely tightly and specifically to other molecules: enzymes to their substrates; antibodies to their antigens; DNA strands to their complementary strands; and so on. Binding can be characterized by a binding constant or association constant (Ka), or its inverse, the dissociation constant (Kd).
binomial nomenclature In biology, each species is generally identified by two terms: the first is the genus to which it belongs, and the second is the specific epithet that distinguishes it from others in that genus (e.g., Quercus suber, cork oak). The genus name always has an initial capital; the specific epithet is never capitalized, even though it may be derived from a proper name (e.g., keranda nut, Elaeocarpus bancroftii). Both terms in the binomial are italicized. Based on the system of classification developed by Carolus Linnaeus.
binomial expansion The probability that an event will occur 0, 1, 2, ..., n times out of n is given by the successive terms of the expression (p + q)n, where p is the probability of the event occurring, and q = 1 - p.
bio- A prefix derived from bios and used in scientific words to associate the concept of "living organisms." Usually written with a hyphen before vowels, for emphasis or in neologisms; otherwise usually without a hyphen.
bio-accumulation In an organism, concentration of materials which are not components critical for that organism's survival. Usually it refers to the accumulation of metals or other compounds (e.g., DDT). Many organisms - plants, fungi, protists, bacteria, etc. - accumulate metals when grown in a solution of them, either as part of their defence mechanism against the poisonous effect of those compounds, or as a side-effect of the chemistry of their cell walls. Bio-accumulation is important as part of the microbial mining cycle (q.v.), removing toxic metals from wastewater, as a purification (bioremediation) process, etc. See also biosorption; microbial mining.
bio-assay A procedure for the assessment of a substance by measuring its effect in living cells or on organisms. Animals have been used extensively in drug research in bio-assays for the pharmacological activity of drugs. However, bio-assays are now usually developed using bacteria or animal or plant cells, as these are usually much easier to handle than whole animals or plants, are cheaper to make and keep, and avoid the ethical problems associated with testing of animals. Sometimes used to detect minute amounts of substances that influence or are essential to growth.
bio-augmentation Increasing the activity of bacteria that decompose pollutants; a technique used in bioremediation.
biocatalysis; biocatalyst Use of enzymes to catalyse chemical reactions. See biotransformation.
biocontrol The control of living organisms (especially pests) by biological means. Any process using deliberately introduced living organisms to restrain the growth and development of other, very often pathogenic, organisms, such as the use of spider mites to control cassava mealy bug, or the introduction of myxomatosis into Australia to control rabbits. The term also applies to use of disease-resistant crop cultivars. Biotechnology approaches biocontrol in various ways, such as using fungi, viruses or bacteria which are known to attack an insect or weed pest.
bioconversion Conversion of one chemical into another by living organisms, as opposed to their conversion by enzymes (which is biotransformation) or by chemical processes. The usefulness of bioconversion is much the same as that of biotransformation - in particular its extreme specificity and ability to work in moderate conditions. However, bioconversion has several other properties, including the possibility of having several chemical steps. A major commercial application is in the manufacture of steroids. The "basic" steroid molecule, often isolated from plants, is itself a very complicated molecule, and not one that is easy to modify by normal chemical means to produce the very specific molecules needed for drug use. However, a particular type of bioconversion that attacks only specific bits of the molecule can be used. Bioconversion is particularly useful for introducing chemical changes at specific points in large, complex molecules.
biodegradable See biodegradation.
biodegradation The breakdown by living organisms of a compound to its chemical constituents. Materials that can be easily biodegraded are colloquially termed biodegradable.
biodiversity 1. The variety of species (species diversity) or other taxa of animals, micro-organisms and plants in a natural community or habitat, or of communities in a particular environment (ecological diversity), or of genetic variation in a species (genetic diversity, q.v.). The maintenance of a high level of biodiversity is important for the stability of ecosystems.
2. The variety of life in all its forms, levels and combinations, encompassing genetic diversity, species diversity and ecosystem diversity. cf agrobiodiversity (Source: FAO, 1999)
bio-energetics The study of the flow and the transformations 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. At one extreme, it can be enormously useful in focusing attention on problems that need to be confronted; at the other extreme, it can become a name-calling argument between the "pro-biotechnology" and "anti-biotechnology" schools of thought, which, as it reduces discussion to epithets and clichés, can make better sound bites.
biofuel A gaseous, liquid or solid fuel that contains energy derived from a biological source. For example, rapeseed oil or fish liver oil can be used in place of diesel fuel in modified engines. A commercial application is the use of modified rapeseed oil, which - as rapeseed methyl ester (RME) - can be used in modified diesel engines, and is sometimes named bio-diesel. cf biogas.
biogas A mixture of methane and carbon dioxide resulting from the anaerobic decomposition of waste such as domestic, industrial and agricultural sewage. a.k.a. gobar.
biogenesis The principle that a living organism can only arise from other living organisms similar to itself and can never originate from non-living material.
bio-informatics The use and organization of information of biological interest. In particular, it is concerned with organizing bio-molecular databases, in getting useful information out of such databases, in utilizing powerful computers for analysing such information, and in integrating information from disparate biological sources.
biolistics (from biological + ballistics) A technique to insert DNA into cells. The DNA is mixed with small metal particles - usually tungsten or gold - a fraction of a micrometre across. These are then fired into a cell at very high speed. They puncture the cell and carry the DNA into the cell. Biolistics has an advantage over transfection, transduction, etc., because it can apply to any cell, or indeed to parts of a cell. Thus use of biolistics has inserted DNA into animal, plant and fungal cells, and into mitochondria inside cells. a.k.a. microprojectile bombardment.
biological ageing See senescence.
biological control See biocontrol.
biological containment Restricting the movement of (genetically engineered) organisms by arranging barriers to prevent them from growing outside the laboratory. Biological containment can take two forms: making the organism unable to survive in the outside environment, or making the outside environment inhospitable to the organism. The latter is rarely suitable for bacteria, which, in principle, could survive almost anywhere. Thus for bacteria and yeasts, the favoured approach is to mutate the genes in the organism so that they require a supply of a specific nutrient that is usually available only in the laboratory. If they get out, they then cannot grow. Making the environment unfriendly to the organism is partly a biological control, partly a physical one. Thus, some of the first genetically engineered rice strains were developed in England (which is too cold for rice to grow) and tried in the field in Arizona (where it is too dry). Biological containment may also involve the use of vector molecules and host organisms which have been genetically disabled such that they can survive only in the peculiar conditions provided by the experimenter and which are unavailable outside the laboratory.
biological diversity See biodiversity. (Source: FAO, 1999)
biomass 1. The cell mass produced by a population of living organisms.
2. The organic mass 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.
biometrics See biometry.
biometry The application of statistical methods to the analysis of biological problems.
biopesticide A compound that kills organisms by virtue of specific biological effects rather than as a broader chemical poison. Specific types include bio-insecticides and bio-fungicides. Bio-pesticides differ from biocontrol agents in that bio-pesticides are passive agents, whereas biocontrol agents are active, seeking out the pest to be destroyed. There are some extremely attractive anti-pest materials, such as Bacillus thuringiensis (Bt) toxin, which specifically interferes with the absorption of food from the guts of some insects but is harmless to mammals. The rationale behind developing bio-pesticides is that they are more likely to be biodegradable and are targeted at specific elements of the pest's metabolism.
biopolymer Any large polymeric molecule (protein, nucleic acid, polysaccharide, lipid) produced by a living organism.
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 growth chamber (fermenter, fermentation vessel) for cells or micro-organisms.
bioremediation A process that uses living organisms to remove contaminants, pollutants or unwanted substances from soil or water. cf bio-augmentation; bio-enrichment.
biosensor A device that uses an immobilized agent (such as an enzyme, antibiotic, organelle or whole cell) to detect or measure a chemical compound. A reaction between the immobilized agent and the molecule being analysed is transduced into an electric signal.
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.
biotechnology 1. The use of biological processes or organisms for the production of materials and services of benefit to humankind. Biotechnology includes the use of techniques for the improvement of the characteristics of economically important plants and animals and for the development of micro-organisms to act on the environment.
2. The scientific manipulation of living organisms, especially at the molecular genetic level, to produce new products, such as hormones, vaccines or monoclonal antibodies.
biotic factor Other living organisms that are a factor of an organism's environment, and form the biotic environment, affecting the organism in many ways.
biotic stress Stress resulting from living organisms which can harm plants, such as viruses, fungi, bacteria, parasitic weeds and harmful insects. cf abiotic stress.
biotin A vitamin of the B complex. It is a co-enzyme for various enzymes that catalyse the incorporation of carbon dioxide into various compounds. It is essential for the metabolism of fats. Biotin is attached to pyruvate carboxylase by a long, flexible chain like that of lipoamide in the pyruvate dehydrogenase complex. Adequate amounts are normally produced by the intestinal bacteria in animals. a.k.a. vitamin H (in USA).
biotin labelling 1. The attachment of biotin to another molecule.
2. The incorporation of a biotin-containing nucleotide into a DNA molecule.
biotinylated-DNA A DNA molecule labelled with biotin by incorporation of biotinylated-dUTP into a DNA molecule. It is used as a non-radioactive probe in hybridization experiments, such as Southern transfer. The detection of the labelled DNA is achieved by complexing it with streptavidin (an antibiotic with a high affinity for biotin) to which is attached a colour-generating agent such as horseradish peroxidase that gives a fluorescent green colour upon reaction with various organic reagents.
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 whole, dead micro-organism that contains an enzyme or several enzymes.
biotope A small habitat in a large community.
biotoxin A naturally produced toxic compound which shows pronounced biological activity and presumably has some adaptive significance to the organism which produces it.
bivalent A pair of synapsed or associated homologous chromosomes (one of maternal origin; the other of paternal origin) that have each undergone duplication. Each duplicated chromosome comprises two chromatids. Thus a bivalent comprises four chromatids.
b-lactamase An ampicillin resistance gene. See selectable marker.
blastocyst (also blastocist) 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).
B lymphocytes; B cells An important class of lymphocytes that mature in bone marrow (in mammals) and the Bursa of Fabricius (in birds), that are largely responsible for the antibody-mediated or humoral immune response; they give rise to the antibody-producing plasma cells and some other cells of the immune system.
bleach A fluid, powder or other whitening (bleaching) or cleaning agent, usually with free chlorine ions. Commercial bleach contains calcium hypochlorite or sodium hypochlorite, and is a common disinfectant used for cleaning working surfaces, tools and plant materials in plant tissue culture and grafting.
bleeding Used to describe the occasional purplish-black coloration of media due to phenolic products given off by (usually fresh) transfers.
blot 1. As a verb, this means to transfer DNA, RNA or protein to an immobilizing matrix.
2. As a noun, it usually refers to the autoradiograph produced during the Southern or northern blotting procedures. The variations on this theme depend on the molecules:
Southern blot: the molecules transferred are DNA molecules, and the probe (q.v.) is DNA.
northern blot: the molecules transferred are RNA, and the probe is DNA.
western blot: the molecules transferred are protein, and the probe is labelled antibody.
Southwestern blot: the molecules transferred are protein, and the probe is DNA.
dot blot: DNA, RNA or protein are dotted directly onto the membrane support, so that they form discrete spots.
colony blot: the molecules (usually DNA) are from colonies of bacteria or yeast growing on a bacteriological plate.
See DNA probes.
blunt end The end of a DNA duplex molecule in which neither strand extends beyond the other. a.k.a. flush end.
blunt-end cut To cleave phospho-diester bonds in the backbone of duplex DNA between the corresponding nucleotide pairs on opposite strands. This cleavage process results in both strands finishing at the same residue, i.e., there are no nucleotide extensions on either strand. a.k.a. flush-end cut.
blunt-end ligation Joining (ligation) of the nucleotides that are at the ends of two blunt-ended DNA duplex molecules.
boring platform Sterile bottom half of a Petri dish used for preparing explants with a cork borer.
bound water Water held by the cell and not released if freezing occurs in the intercellular space. cf free water.
bovine somatotrophin (BST) (also bovine somatotropin) a.k.a. bovine growth hormone, this protein is found naturally in cattle, and is the bovine counterpart of human growth hormone, one of the earliest biopharmaceutical products. 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.
bovine spongiform encephalopathy (BSE) a.k.a. mad cow disease. See proteinaceous infectious particle.
bp Abbreviation for base pair, q.v.
bract A modified leaf that subtends flowers or inflorescences and may appear to be a petal.
breed Noun: In AnGR, either (i) 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 or (ii) a group of domestic livestock for which geographical and/or cultural separation from phenotypically similar groups has led to acceptance of its separate identity. cf breed at risk; breed not at risk; critical breed; critical-maintained breed; endangered-maintained breed. (Source: FAO, 1999)
breed at risk In AnGR: Any breed that may become extinct if the factors causing its decline in numbers are not eliminated or mitigated. (Source: FAO, 1999)
Breeds may he in danger of becoming extinct for a variety of reasons. Risk of extinction may result from, inter alia, low population size; direct and indirect impacts of policy at the farm, country or international levels; lack of proper breed organization; or lack of adaptation to market demands. Breeds are categorized as to their risk status on the basis of, inter alia, the actual numbers of male and/or female breeding individuals and the percentage of pure-bred females. FAO has established categories of risk status: critical, endangered, critical-maintained, endangered-maintained, and not-at-risk. (Source: FAO, 1999)
breeding The process of sexual reproduction and production of offspring.
breeding value In quantitative genetics, the part of the deviation of an individual phenotype from the population mean that is due to the additive effects of alleles. In practical terms: if an animal is mated with a random sample of animals from a population, that animal's breeding value for a certain trait is twice the average deviation of its offspring from the population mean for that trait.
breed not at risk In AnGR: A breed where the total number of breeding females and males is greater than l 000 and 20 respectively; or the population size approaches 1 000 and the percentage of pure-bred females is close to 100%, and the overall population size is increasing. cf breed at risk. (Source: FAO, 1999)
brewing The process by which beer is made. In the first stage the barley grain is soaked in water and allowed to germinate (malting), during which the natural enzymes of the grain convert the seed starch to maltose, and then to glucose. Grain is then dried, crushed, and added to water at a specific temperature (steeping) and any remaining starch is converted to sugar. The resulting liquid (wort) is the raw material to which yeast is added to convert sugar to alcohol. Hops (female flowers of Humulus lupulus) are added during this process to give a characteristic flavour.
brewer's yeast Strains of yeast, often Saccharomyces cerevisiae, that are used in 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 In quantitative genetics, the proportion of the total phenotypic variation due to genetic variation.
browning Discoloration due to phenolic oxidation of freshly cut surfaces of explant tissue. In later stages of culture, such discoloration may indicate a nutritional or pathogenic problem, generally leading to necrosis.
brucellosis Disease caused by infection with organisms of the genus Brucella.
BSE Bovine spongiform encephalopathy. See proteinaceous infectious particle.
BST See bovine somatotrophin.
Bt See Bacillus thuringiensis.
bubble column fermenter A fermentation vessel, or 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; generally protected by modified scale leaves. A terminal (or apical) bud exists at the tip of a stem or branch, while axillary (or lateral) buds develop in the axils of leaves.
bud scar A scar left on a shoot when the bud or bud scales drop.
bud sport A somatic mutation arising in a bud and producing a genetically different shoot. Bud sports includes changes due to gene mutation, somatic reduction, chromosome deletion 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 yeast Saccharomyces cerevisiae.
3. A form of grafting 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. See grafting.
buffer A solution that resists change in pH when an acid or alkali is added, or when solutions are diluted.
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 a characteristic buoyant density, which reflects the proportion of G=C base pairs. The greater the proportion of G=C, the greater the buoyant density of the DNA.