Glossary

Genetics glossary

914 definitions · page 7 of 16.

Duchenne muscular dystrophy: A lethal muscle disease in humans caused by mutation in a huge gene coding for the muscle protein dystrophin; inherited as an X-linked recessive phenotype.
duplicate gene: An identical locus mapping to a second site in a genome.
duplication: More than one copy of a particular chromosomal segment in a chromosome set. Duplications supply genetic material capable of evolving new functions.
dyad: Two sister chromatids attached to the same centromere. A pair of sister chromatids joined at the centromere, as in mitosis and meiosis.
E (exit site): Site on the ribosome through which tRNAs pass after they have donated their amino acid to the growing nascent polypeptide chain. ecdysone
ecdysone: A moulting hormone in insects.
ectopic expression: The occurrence of gene expression in a tissue in which it is normally not expressed. Such ectopic expression can be caused by the juxtaposition of novel enhancer elements to a gene during genetic manipulation of transgenic organisms.
ectopic integration: In a transgenic organism, the insertion of an introduced gene (transgene) at a site other than its usual locus.
electrophoresis: A technique for separating the components of a mixture of charged molecules (proteins, DNAs, or RNAs) in an electric field within a gel or other support. The movement of electrically charged molecules in an electric field often resulting in their separation.
electroporation: A technique for transfecting cells by the application of a high-voltage electric pulse.
elongation factors (EF-Ts EF-Tu EF-G): Proteins necessary for the proper elongation and translocation processes during translation at the ribosome in prokaryotes. Replaced by eEF1 and eEF2 in eukaryotes.
elongation factors (EF-Ts, EF-Tu, EF-G): Proteins necessary for the proper elongation and translocation processes during translation at the ribosome in prokaryotes. Replaced by eEF1 and eEF2 in eukaryotes.
embryonic (or tissue) polarity: The production of axes of asymmetry in a developing embryo or tissue primordium.
endogenote: Bacterial host chromosome. See merozygote.
endomitosis: Chromosomal replication without nuclear or cellular division that results in cells with many copies of the same chromosome.
endonuclease: An enzyme that cleaves or hydrolyzes phosphodiester bonds within a polynucleotide chain.
endopolyploidy: An increase in the number of chromosome sets caused by replication without cell division.
endosperm: Triploid tissue in a seed, formed from fusion of two haploid female and one haploid male nucleus.
enforced outbreeding: Deliberate avoidance of mating between relatives.
enhancer: A cis-regulatory sequence that can elevate levels of transcription from an adjacent promoter. Many tissue specific enhancers can determine spatial patterns of gene expression in higher eukaryotes. Enhancers can act on promoters over many tens of kilobases of…
enhancer trap: A transgenic construction inserted in a chromosome which is used to identify tissue-specific enhancers in the genome. In such a construct, a promoter sensitive to enhancer regulation is fused to a reporter gene, such that expression patterns of the reporter…
enucleate cell: A cell having no nucleus.
environment: The combination of all the conditions external to the genome that potentially affect its expression and its structure.
environmental variance: The variance due to environmental variation.
enzyme: A protein that functions as a catalyst. Protein catalyst.
episome: A genetic element in bacteria that can replicate free in the cytoplasm or can be inserted into the main bacterial chromosome and replicate with the chromosome. Term used by Jacob and Wollman for genetic elements that can either exist independently in a cell…
epistasis: The masking of the phenotypic effect of alleles at one gene by alleles of another gene. A situation in which the phenotypic expression of a genotype at one locus depends upon the genotype at another locus.
equational division: The second meiotic division is an equational division because it does not reduce chromosome numbers. A nuclear division that maintains the same ploidy level of the cell.
equivalence group: A set of immature cells that all have the same developmental potential. In many cases cells of an equivalence group end up adopting different fates from one another.
ethidium: A molecule that can intercalate into DNA double helices when the helix is under torsional stress.
euchromatin: A chromosome region that stains poorly or not at all; thought to contain the normally functioning genes. Region of eukaryotic chromosome that is diffuse during interphase. Presumably the actively transcribing DNA of the chromosomes. (See heterochromatin)
eugenics: Controlled human breeding based on notions of desirable and undesirable genotypes.
eukaryote: An organism having eukaryotic cells with true nuclei.
eukaryotic cell: A cell containing a nucleus.
euploid: A cell having any number of complete chromosome sets, or an individual composed of such cells.
euploidy: The condition of a cell or organism that has one or more complete sets of chromosomes.
evolution: In Darwinian terms a gradual change in phenotypic frequencies in a population that results in individuals with improved reproductive success.
evolutionary rate: The rate of divergence between taxonomic groups measurable as amino acid substitutions per million years.
excision repair: A process whereby cells remove part of a damaged DNA strand and replace it through DNA synthesis using the undamaged strand as a template. The repair of a DNA lesion by removal of the faulty DNA segment and its replacement with a new segment.
exconjugant: Each of the two cells that separates after conjugation has taken place. A female bacterial cell that has just been in conjugation with a male and that contains a fragment of male DNA.
exogenote: DNA that a bacterial cell has taken up through one of its sexual processes. See merozygote.
exon: A region of a gene that is present in the final functional transcript (mRNA) from that gene. Any non-intron section of the coding sequence of a gene; together the exons constitute the mRNA and are translated into protein.
exon shuffling: The hypothesis put forward by Walter Gilbert that exons code for functional units of a protein and that evolution of new genes has proceeded by recombination or exclusion of exons.
exonuclease: An enzyme that cleaves nucleotides one at a time from an end of a polynucleotide chain. An enzyme that hydrolyzes phosphodiester bonds from either the 3' or 5' terminus of a polynucleotide molecules.
experimental design: A branch of statistics that attempts to outline the way in which experiments should be carried out so the data gathered will have statistical value.
exploitation competition: A form of competition that revolves around the superior ability to gather resources rather than an active interaction among organisms for these resources.
expressed sequence tag (EST): A unique DNA sequence derived from a cDNA library (therefore from a sequence which has been transcribed in some tissue or at some stage of development). The EST can be mapped, by a combination of genetic mapping procedures, to a unique locus in the genome…
expression vector: A vector that has been designed to express cloned genes in a particular cell type.
expressivity: The degree to which a particular genotype is expressed in the phenotype. The degree of expression of a genetically controlled trait.
F (prime) factor: A fertility factor into which a portion of the bacterial chromosome has been incorporated.
F+(plus) cell: In Escherichia coli, a cell having a free fertility factor; a male cell.
F-(minus) cell: In Escherichia coli, a cell having no fertility factor; a female cell.
f-pili: Sex pili. Hair-like projections on an F+, an F' or Hfr bacterium involved in anchorage during conjugation and presumably through which DNA passes.
F1 generation: The first filial generation, produced by crossing two parental lines.
F2 generation: The second filial generation, produced by selfing or intercrossing the F1.
factorial: The product of all integers from the specified number down to one (unity).
facultative heterochromatin: Heterochromatin located in positions that are composed of euchromatin in other individuals of the same species, or even in the other homologue of a chromosome pair.
familial trait: A trait shared by members of a family.
family selection: A breeding technique of selecting a pair on the basis of the average performance of their progeny.
Fanconi s anemia: An heritable disease in human beings with a syndrome of congenital malformations (decreased blood cells, short stature, patchy dark skin pimentation, predisposition to cancer especially leukaemia) inherited as an autosomal recessive.