Eeffective population size -- The number of individuals in a population that have an equal probability of contributing gametes to the next generation.effector molecule -- Small, biologically active molecule that acts to regulate the activity of a protein by binding to a specific receptor site on the protein.electrophoresis -- A technique used to separate a mixture of molecules by their differential migration through a stationary phase (such as a gel) in an electrical field.endocytosis -- The uptake by a cell of fluids, macromolecules, or particles by pinocytosis, phagocytosis, or receptor-mediated endocytosis.endomitosis -- Chromosomal replication that is not accompanied by either nuclear or cytoplasmic division.endonuclease -- An enzyme that hydrolyzes internal phosphodiester bonds in a polynucleotide chain or nucleic acid molecule.endoplasmic reticulum -- A membranous organelle system in the cytoplasm of eukaryotic cells. The outer surface of the membranes may be ribosome-studded (rough ER) or smooth ER.endopolyploidy -- The increase in chromosome sets that results from endomitotic replication within somatic nuclei.endosymbiont theory -- The proposal that self-replicating cellular organelles such as mitochondria and chloroplasts were originally free-living organisms that entered into a symbiotic relationship with nucleated cells.enhancer -- Originally identified as a 72-bp sequence in the genome of the virus, SV40, that increases the transcriptional activity of nearby structural genes. Similar sequences that enhance transcription have been identified in the genomes of eukaryotic cells. Enhancers can act over a distance of thousands of base pairs and can be located 5', 3' or internal to the gene they affect, and thus are different from promoters.environment -- The complex of geographic, climatic, and biotic factors within which an organism lives.enzyme -- A protein or complex of proteins that catalyzes a specific biochemical reaction.epigenesis -- The idea that an organism develops by the appearance and growth of new structures. Opposed to preformationism, which holds that development is the growth of structures already present in the egg.episome -- A circular genetic element in bacterial cells that can replicate independently of the bacterial chromosome or integrate and replicate as part of the chromosome.epistasis -- Nonreciprocal interaction between genes such that one gene interferes with or prevents the expression of another gene. For example, in Drosophila, the recessive gene eyeless, when homozygous, prevents the expression of eye color genes present in the genome.epitope -- That portion of a macromolecule or cell that acts to elicit an antibody response; an antigenic determinant. A complex molecule or cell can contain several such sites.equational division -- A division of each chromosome into longitudinal halves that are distributed into two daughter nuclei. Chromosome division in mitosis is an example of equational division.equatorial plate -- See metaphase plate.euchromatin -- Chromatin or chromosomal regions that are lightly staining and are relatively uncoiled during the interphase portion of the cell cycle. Euchromatic regions contain most of the structural genes.eugenics -- The improvement of the human species by selective breeding. Positive eugenics refers to the promotion of breeding of those with favorable genes, and negative eugenics refers to the discouragement of breeding among those with undesirable traits.eukaryotes -- Those organisms having true nuclei and membranous organelles and whose cells demonstrate mitosis and meiosis.euphenics -- Medical or genetic intervention to reduce the impact of defective genotypes.euploid -- Polyploid with a chromosome number that is an exact multiple of a basic chromosome set.evolution -- The origin of plants and animals from preexisting types. Descent with modifications.excision repair -- Removal of damaged DNA segments followed by repair. Excision can include the removal of individual bases (base repair) or a stretch of damagednucleotides (nucleotide repair). The gap created by excision is filled by polymeraseand the ends are ligated to form an intact molecule.exon (extron) -- The DNA segment(s) of a gene that are transcribed and translated into protein.exonuclease -- An enzyme that breaks down nucleic acid molecules by breakingthe phosphodiester bonds at the 3' or 5' terminal nucleotides.expressed sequence tags (ESTs) -- All or part of the nucleotide sequence of cDNA clones. Used as markers in construction of genetic maps.expression vector -- Plasmids or phages carrying promoter regions designed tocause expression of inserted DNA sequences.expressivity -- The degree or range in which a phenotype for a given trait isexpressed.extranuclear inheritance -- Transmission of traits by genetic information containedin cytoplasmic organelles such as mitochondria and chloroplasts.ecdysone 蜕皮激素：昆虫中的一种蜕皮的激素。