Glossary

Genetics glossary

914 definitions · page 5 of 16.

concordance: The amount of similarity in phenotype between individuals.
conditional mutation: A mutation that has the wild-type phenotype under certain (permissive) environmental conditions and a mutant phenotype under other (restrictive) conditions.
conditional-lethal mutation: A mutation that is lethal under one condition but not lethal under another condition.
confidence limits: A statistical term for a pair of numbers that predict the range of values within which a particular parameter lies for a given level of confidence (probability).
conjugation: A process whereby two cells come in contact and exchange genetic material. In prokaryotes the transfer is a one-way process. The union of two bacterial cells, during which chromosomal material is transferred from the donor to the recipient cell. Conjugation…
consanguineous: Meaning between blood relatives ; usually refers to inbreeding or incestuous matings.
consensus sequence: A sequence of nucleotides or amino acids in common between regions of homology in different but related DNA or RNA or protein sequences.
conservative replication: A postulated mode of DNA replication in which an intact double helix acts as a template for a new double helix; known to be incorrect. A disproved model of DNA synthesis suggesting that one-half of the daughter DNA molecules should have both strands composed…
conserved sequence: An invariant sequence found in different DNA or RNA or protein sequences.
constant region: A region of an antibody molecule that is nearly identical with the corresponding regions of antibodies of different specificities.
constitutive: Always expressed in an unregulated fashion (when referring to gene control).
constitutive heterochromatin: Heterochromatin that surrounds the centromere. Specific regions of heterochromatin always present and in both homologs of a chromosome. See satellite DNA.
constitutive mutation: A mutation which causes transcription to be no longer under regulatory control.
continuous replication: The uninterrupted replication of DNA in the 5' to 3' direction using a 3' to 5' template.
continuous variation: Variation measured on a continuum rather than in discrete units or categories (eg height in human beings).
controlling element: A term used by maize geneticists to indicate a mobile genetic element capable of producing an unstable mutant target gene; two types exist, the regulator and the receptor elements.
copper fist: Configuration of a DNA-binding protein that resembles a fist closed around a penny. In this case the penny is copper ions; the knuckles of the fist of the yeast ACE1 protein interact with the promoter of the metallothionein gene, enhancing its transcription.
copy-choice hypothesis: An incorrect hypothesis that stated that recombination resulted from the switching of the DNA-replicating enzyme from one DNA homologue to the other.
copy-choice model: A model of the mechanism for crossing over, suggesting that crossing over occurs during chromosome division and can occur only between two supposedly new nonsister chromatids; the experimental evidence does not support this model.
corepressor: The metabolite that when bound to the repressor (of a repressible operon) forms a functional unit that can bind to its operator and block transcription.
correction: The production (possibly by excision and repair) of a properly paired nucleotide pair from a sequence of hybrid DNA that contains a mismatched base pair. See mismatch repair
correlation coefficient: A statistic that gives a measure of how closely two variables are related. A statistical measure of the extent to which variations in one variable are related to variations in another.
cosegregation: The tendency for closely linked genes and genetic markers to segregate (be inherited) together.
cosmid: A hybrid plasmid that contains cos sites at each end. Cos sites are recognized during head filling of lambda phages. Cosmids are useful for cloning large segments of foreign DNA (up to 50 kb).
cot value: (cot1/2); The product of Co (the original concentration of denatured DNA) and t (time in seconds), giving a useful index of DNA renaturation. Cot1/2 is the value when 50% renaturation has occurred which can be used to estimate the length of unique DNA in a…
cotransduction: The simultaneous transduction of two or more genes. The simultaneous transduction of two bacterial marker genes.
cotransformation: The simultaneous transformation of two bacterial marker genes.
coupling: Arrangement of wild-type and mutant alleles at two linked loci in which both mutants are on the same chromosome and both wild-type alleles on the homologue (ab/AB). See repulsion
coupling conformation: Linked heterozygous gene pairs in the arrangement, AB/ab.
covariance: A statistical measure used in computing the correlation coefficient between two variables; the covariance is the mean of (x- x(bar))(y-y(bar)) over all pairs of values for the variables x and y, where x(bar) is the mean of the x values and y(bar) is the mean…
cpDNA: Chloroplast DNA.
cri-du-chat syndrome: A non-lethal human condition in infants caused by deletion of part of one homologue of chromosome 5.
crisscross inheritance: Transmission of a gene from male parent to female child to male grandchild for example, X-linked inheritance.
cross: The deliberate mating of two parental types of organisms in genetic analysis.
crossbreed: Fertilization between separate individuals.
crossing over: A process in which homologous chromosomes exchange parts normally reciprocally but sometimes unequally. The exchange of corresponding chromosome parts between homologues by breakage and reunion of DNA molecules normally during prophase I of meiosis but also…
crossover suppression: Reduction of crossing over within an inversion loop in inversion heterozygotes due to physical constraints during synapsis. Crossing over within an inversion loop, when it does occur, leads to defective (deleted and duplicated) crossover chromosomes and…
cruciform configuration: A region of DNA having a sequence at one end repeated but inverted at the other end, so that each strand may pair with itself to form a helix extending sideways from the main helix.
cryptic coloration: Coloration that allows an organism to match its background and hence become less vulnerable to predation or recognition by prey.
culture: Tissue or cells multiplying by asexual division, grown for experimentation.
cyclic AMP (cAMP): A form of AMP (adenosine monophosphate) used frequently as a second messenger in eukaryotics and in catabolite repression in prokaryotes.
Cys: Cysteine (an amino acid).
cystic fibrosis (CF): A potentially lethal human disease of secretory cells, showing excess lung mucus secretion, and inherited as an autosomal recessive on chromosome 7. CF is caused by mutations in a gene encoding the cystic fibrosis membrane conductance regulator, a…
cytidine: The nucleoside containing cytosine as its base.
cytochrome: A class of protein, found in mitochondrial membranes, whose main function is oxidative phosphorylation of ADP to form ATP.
cytogenetics: The cytological approach to genetics, mainly involving microscopic studies of chromosomes.
cytohet: A cell containing two genetically distinct types of a specific organelle.
cytokinesis: The division of the cytoplasm of a cell into two daughter cells. See karyokinesis.
cytoplasm: The material between the nuclear and cell membranes; includes fluid (cytosol) organelles, and various membranes.
cytoplasmic inheritance: Inheritance via genes found in cytoplasmic organelles. Extra-chromosomal inheritance controlled by non-nuclear genomes.
cytosine: A pyrimidine base that pairs with guanine. See pyrimidine.
cytosol: The fluid portion of the cytoplasm, outside the organelles.
cytotoxic T lymphocyte (Tc): T lymphocyte responsible for attacking cancerous host cells or cells infected with an invading bacterium or virus.
d-loop: Configuration found during DNA replication of chloroplast and mitochondrial chromosomes wherein the origin of replication is different on the two strands. The first structure formed is a displacement loop or D-loop.
Darwinian fitness: The relative probability of survival and reproduction for a genotype. see fitness.
dauermodification: The persistence for several generations of an environmentally induced trait.
deficiency: The absence of part of the normal genome or chromosome set. See deletion.
degenerate code: A code in which several code words have the same meaning. The genetic code is degenerate because there are many instances in which different codons specify the same amino acid. A genetic code in which some amino acids may each be encoded by more than one…
degrees of freedom: An estimate of the number of independent categories in a particular statistical test or experiment.
deletion: Loss of a DNA (chromosome) segment from a chromosome. Deletions are recognised genetically by: 1. absence of reverse mutation 2. presence of a deletion loop at meiosis visualized cytologically 3. revealing of recessive lethals 4. pseudodominance