ABC modelWidely accepted model of flower organ identity that appears generally applicable to distantly related dicotyledon ous, although less well to monocotyledon…
Abiotic stressOutside (nonliving) factors which can cause harmful effects to plants, such as soil conditions, drought, extreme temperatures.
abscisic acidA phytohormone implicated in the control of many plant responses to abiotic stress, such as extent of stomatal opening under water deficit (i.e.
acaricideA pesticide used to kill or control mites or ticks.
ACC synthaseAbbreviation for 1-aminocyclopropane-1-carboxylase. The enzyme catalyses the rate limiting step in the ethylene biosynthetic pathway, and is particularly…
acceptor controlThe regulation of the rate of respiration by the availability of ADP as a phosphate acceptor.
acceptor junction siteThe junction between the 3' end of an intron and the 5' end of an exon. See: donor junction site.
accessory budA lateral bud occurring at the base of a terminal bud or at the side of an axillary bud.
acclimatizationThe adaptation of a living organism (plant, animal or micro-organism) to a changed environment that subjects it to physiological stress.
acellularTissues or organisms that are not made up of separate cells but often have more than one nucleus.
acetyl co-enzyme A(Abbreviation: acetyl CoA) A compound formed in the mitochondria when an acetyl group (CH3CO-) - derived from breakdown of fats, protein s, or…
acquiredDeveloped in response to the environment, not inherited, such as a character trait (acquired characteristic) resulting from environmental effect(s).
acridine dyesA class of positively charged polycyclic molecules that intercalate into DNA and induce frameshift mutations.
acrocentricA chromosome that has its centromere near the end.
acropetalArising or developing in a longitudinal sequence beginning at the base and proceeding towards the apex. Opposite: basipetal.
activated charcoalCharcoal that has been treated to remove hydrocarbons and to increase its adsorptive properties.
Active transportThe movement of a molecule or groups of molecules across a cell membrane, which requires the expenditure of cellular energy, because the direction of…
acyl carrier protein(Abbreviation: ACP). A class of molecules that bind acyl intermediates during the formation of long-chain fatty acids.
AdaptationAdjustment of a population to changes in environment over generations, associated (at least in part) with genetic changes resulting from selection imposed…
Adaptive radiationThe evolution of new species or sub- species to fill unoccupied ecological niches.
additive genesGenes whose net effect is the sum of their individual allelic effects, i.e. they show neither dominance nor epistasis.
additive genetic varianceThe net effect of the expresson of additive genes, and thus the chief cause of the resemblance between relatives.
adenine(Abbreviation: A). One the base s found in DNA and RNA. See: adenosine.
adenosineThe (ribo)nucleoside resulting from the combination of the base adenine (A) and the sugar D-ribose.
Agarose gel electrophoresisA matrix composed of a highly purified form of agar that is used to separate larger DNA and RNA molecules ranging 20,000 nucleotides. (See Electrophoresis.
Aggregate1. 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.
agonistA drug that triggers an action from a cell or another drug.
AgrobacteriumA genus of bacteria that includes several plant pathogenic species, causing tumour-like symptoms. See: Agrobacterium rhizogenes, Agrobacterium tumefaciens.
Agrobacterium rhizogenesA bacterium that causes hairy root disease in some plants. Similar to the crown gall disease caused by Agrobacterium tumefaciens, this is achieved by the…
Agrobacterium tumefaciensA bacterium that causes crown gall disease in some plants. The bacterium characteristically infects a wound, and incorporates a segment of Ti plasmid DNA…
Agrobacterium tumefaciens-mediated transformationThe process of DNA transfer from Agrobacterium tumefaciens to plants, that occurs naturally during crown gall disease, and can be used as a method of…
airlift fermenterA 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…
albinism(AL-bye-niz-em) A group of genetic conditions marked by little or none of the pigment melanin in the skin, hair, and/or eyes.
albino1. An organism lacking pigmentation, due to genetic factors. The condition is albinism 2. A conspicuous plastid mutant involving loss of chlorophyll.
aleuroneThe outermost layer of the endosperm in a seed, and the site of enzymes concerned with endosperm digestion during seedling growth.
algal biomassSingle-celled plants (e.g. Chlorella spp. and Spirulina spp.) grown commercially in ponds to make feed materials for zooplankton, which are in turn…
alkylating agent(AL-kuh-LAY-ting AY-jent) A type of drug that is used in the treatment of cancer. It interferes with the cell's DNA and inhibits cancer cell growth.
alleleA 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).
allele frequencyThe 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…
allele-specific amplification(Abbreviation: ASA). The use of the polymerase chain reaction at a sufficiently high stringency that only one allele is amplified.
AllelesAlternate forms of a gene or DNA sequence, which occur on either of two homologous chromosomes in a diploid organism. (See DNA polymorphism.)
AllelopathyThe secretion of chemicals, such as phenolic and terpenoid compounds, by a plant's roots, which inhibit the growth or reproduction of competitor plants.
allergen(AL-er-jen) A substance that causes an allergic response. Examples include pollen, molds, and certain foods.
allogamyCross fertilization in plants. See: fertilization.
allogenicTaken from different individuals of the same species. Also called allogeneic.
allometricWhen the growth rate of one part of an organism differs from that of another part or of the rest of the body.
AllopatricIn the context of natural populations of animals or plants, inhabiting distinct and separate areas.
allopatric speciationSpeciation occurring at least in part because of geographic isolation.
allopolyploidA polyploid organism with sets of chromosomes derived from different species. Opposite: autopolyploid.
allosteric enzymeAn enzyme that has two structurally distinct forms, one of which is active and the other inactive.
allosteric regulationA 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 siteThat part of an enzyme molecule where the non-covalent binding of an effector molecule can affect the enzyme's catalytic activity.
allosteric transitionA 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…
allotetraploidAn allopolyploid having two different progenitor genomes.
allotypeA classification of antibody molecules according to the antigenicity of the constant regions; a variation that is determined by a single allele.
allozygoteA individual that is heterozygous for two different mutant allele s.
Alternative mRNA splicingThe inclusion or exclusion of different exons to form different mRNA transcripts. (See RNA.)
Alu sequencesA highly repeated family of 300-bp long sequences dispersed throughout the human genome, so named because they are released by the digestion of genomic…