| 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 |
| 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. |
| 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 DNA and can be 5' or 3' to the promoter they regulate. A eukaryotic
DNA sequence that increases transcription of a region even if the
enhancer is distant from the region being transcribed. |
| 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 gene identify the spatial regulation conferred by
nearby enhancers. |
| 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 or become integrated into the host chromosome. |
| 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 and serves to identify that gene locus. |
| 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. |
