Glossary

Genetics glossary

914 definitions · page 2 of 16.

anti-oncogene: A gene that prevents malignant (cancerous) growth and whose absence, by mutation, results in malignancy (eg retinoblastoma).
antibody: A protein produced by a B lymphocyte that protects the organism against an antigen. A protein (immunoglobulin) molecule, produced by the immune system, that recognizes a particular foreign antigen and binds to it; if the antigen is on the surface of a cell…
anticoding strand: The DNA strand that forms the template for both the transcribed mRNA and the coding DNA strand.
anticodon: The three-base sequence in tRNA complementary to a codon on mRNA. A nucleotide triplet in a tRNA molecule that aligns with a particular codon in mRNA under the influence of the ribosome, so that the amino acid carried by the tRNA is added to a growing…
antigen: A molecule whose shape triggers the production of antibodies (immunoglobulins) that will bind to the antigen. A foreign substance capable of triggering an immune response in an organism.
antimorph: A mutant expressing some agent that antagonizes a normal gene product.
antimutator mutation: mutation of DNA polymerase that decreases the overall mutation rate.
antiparallel: A term used to describe the opposite orientations of the two strands of a DNA double helix; the 5' end of one strand aligns with the 3' end of the other strand.
antisense RNA: RNA product of mic (mRNA-interfering complementary RNA) genes that regulates another gene by base pairing with and thus preventing translation from its mRNA.
antiterminator protein: A protein that, when bound at its normal attachment sites in DNA, lets RNA polymerase read through normal terminator sequences (eg the N- and Q-gene products of phage lambda).
AP endonuclease: endonuclease that initiates excision repair at apurinic and apyrimidinic sites on DNA.
AP site: Apurinic or apyrimidinic site resulting from the loss of a purine or pyrimidine residue from the DNA.
Arg: Arginine (an amino acid).
ascospore: A sexual spore from certain fungus species in which spores are found in a sac called an ascus. Haploid spores found in the asci of Ascomycete fungi.
ascus: In fungi, a sac that encloses a tetrad or an octad of ascospores. The sac in Ascomycete fungi that holds the ascospores.
Asn: Asparagine (an amino acid).
Asp: Aspartate (an amino acid).
assignment test: A test that determines whether a locus is on a specific human chromosome by observation of the concordance of the locus and the specific chromosome in a panel of human-mouse hybrid cell lines containing only one or a few of the normal set (22 autosomes, X…
assortative mating: The mating of individuals with similar phenotypes.
ataxia-telangiectasia: A disease (loss of muscle control, and reddening of the skin) in human beings caused by a defect in DNA repair mechanisms induced by ionising radiation (X-rays, beta and alpha particles, gamma rays).
ATP: (adenosine triphosphate) The energy molecule of cells, synthesized mainly in mitochondria and chloroplasts; energy from the breakdown of ATP drives many important reactions in the cell.
attached X: A pair of Drosophila X chromosomes joined at one end and inherited as a single unit.
attenuator: A control region at the promoter end of repressible amino acid operons that exerts transcriptional control based on the translation of a small leader peptide gene. A region adjacent to the structural genes of the trp (tryptophan) operon; in the presence of…
attenuator stem: A configuration of the leader transcript that signals transcription termination in attenuator-controlled amino acid operons.
autogamy: nuclear reorganization in a single Paramecium cell similar to the changes that occur during conjugation.
autonomous replication sequence (ARS): A segment of a DNA molecule necessary for the initiation of its replication; generally a site recognized and bound by the proteins of the replication system.
autopolyploid: A polyploid formed from the doubling of a single genome. Polyploidy in which all the chromosomes come from the same species.
autoradiography: A process by which radioactive materials, often though not exclusively incorporated into cell structures, are located by exposure to a photographic emulsion forming a pattern on the film corresponding to the location of the radioactive compounds within the…
autoregulation: The control of the transcription of a gene by its own gene product.
autosomal set: The non-sex chromosomes consisting of one from each homologous pair in a diploid species.
autosome: Any chromosome that is not a sex chromosome.
autotroph: Organism that is able to utilize carbon dioxide as a carbon source.
autozygosity: homozygosity in which the two alleles are identical by descent (ie they are copies of an ancestral gene) .
auxotroph: An organism with specific nutritional requirements.
auxotrophic mutant: A mutant strain of microorganism that will proliferate only when the medium is supplemented with some specific substance not required by wild-type organisms.
axoneme: A bundle of microtubules and other proteins forming the core of each cilium or flagellum.
B form DNA: A right-handed double-helical conformation of DNA normally seen in solution described by Watson and Crick. A second DNA conformation (A form) is seen in unhydrated DNA (fibres or crystals of oligonucleotides).
bacillus: A rod-shaped bacterium.
back mutation: The process that causes reversion. A change in a nucleotide pair in a mutant gene that restores the original sequence and hence the original phenotype.
backcross: The cross of an individual with one of its parents or an organism with the same genotype as a parent.
bacterial lawn: A continuous cover of bacteria on the surface of a growth medium.
bacteriophage(phage): A virus that infects bacteria.
balanced lethal system: An arrangement of recessive lethal alleles that maintains a heterozygous chromosome combination. homozygotes for any lethal-bearing chromosome perish.
balanced polymorphism: Stable genetic polymorphism maintained by natural selection.
Balbiani ring: A large chromosome puff. The larger polytene chromosomal puffs. See chromosome puff.
Barr body: A densely staining mass that represents an inactivated X chromosome. Heterochromatic body found in the nuclei of normal females but absent in the nuclei of normal males.
basal body: A short cylindrical array of microtubules and other proteins, found at the base of a eukaryotic cilium or flagellum, that organises the assembly of the axoneme (the bundle of microtubules and other proteins forming the core of each cilium or flagellum).
base analogue: A chemical whose molecular structure mimics that of a DNA base; because of the mimicry, the analogue may act as a mutagen.
Batesian mimicry: Form of mimicry in which an innocuous mimic species gains protection by resembling noxious or dangerous model species.
bead theory: The disproved hypothesis that genes are arranged on the chromosome like beads on a necklace, indivisible into smaller units of mutation and recombination.
beta-galactosidase: The enzyme that splits lactose into glucose and galactose (coded by a gene (lac z) in the lac operon of Escherichia coli).
beta-galactoside acetyltransferase: An enzyme that is involved in lactose metabolism and encoded by a gene (lac a) in the lac operon of Escherichia coli).
beta-galactoside permease: An enzyme involved in concentrating lactose in the cell (coded by a gene (lac y) in the lac operon of Escherichia coli)).
bimodal distribution: A statistical distribution having two modes.
binary fission: The process in which a parent cell splits into two daughter cells of approximately equal size. Simple cell division in single-celled organisms.
binomial expansion: The terms generated when a binomial expression [eg. (p+q)] is raised to a particular power n [eg. (p+q)^n].
binomial theorem: The theorem that gives the terms of the expansion of a binomial expression [eg. (p+q)] raised to a particular power n [eg. (p+q)^n].
biochemical genetics: The study of the relationships between genes and enzymes, specifically the role of genes in controlling the steps in biochemical pathways.
biolistic: A method (biological ballistics) of transfecting cells by bombarding them with microprojectiles coated with DNA.
biological species concept: Organisms are classified in the same species if they are potentially capable of interbreeding and producing fertile offspring.