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DictionarySeepolymorphismGenetic Polymorphism
Genetic Polymorphism the coexistence within a population of two or more different hereditary forms, which are in dynamic equilibrium for several or even many generations. Genetic polymorphism is most often caused either by the varying pressures and vectors (direction) of selection under different conditions (for example, at different seasons) or by the increased relative viability of heterozygotes. One type of genetic polymorphism—balanced genetic polymorphism—is characterized by a constant optimal correlation between polymorphic forms, deviation from which proves unfavorable for the species. Balanced genetic polymorphism regulates itself automatically (an optimal correlation of forms is established). The majority of genes in man and animals are in a state of balanced genetic polymorphism. Several forms of genetic polymorphism may be distinguished; analysis of these forms makes it possible to determine the effect of selection in natural populations. REFERENCETimofeev-Resovskii, N. V., and Iu. M. Svirezhev. “O geneticheskom polimorfizme v populiatsiiakh.” Genetika, 1967, no. 10.genetic polymorphism
polymorphism [pol″e-mor´fizm] the ability to exist in several different forms.balanced polymorphism an equilibrium mixture of homozygotes and heterozygotes maintained by natural selection against both homozygotes.genetic polymorphism the occurrence together in the same population of two or more genetically determined phenotypes in such proportions that the rarest of them cannot be maintained merely by recurrent mutation.single nucleotide polymorphism (SNP) a genetic polymorphism between two genomes that is based on deletion, insertion, or exchange of a single nucleotide.ge·net·ic pol·y·mor·phismthe occurrence in the same population of multiple discrete alletic states of which at least two have high frequency (conventionally of 1% or more).genetic polymorphism or polymorphism the presence in a population of two or more MORPHS, produced when different alleles of a gene occur in the same population and the rarest allele is not maintained merely by repeated MUTATION (i.e. has a frequency higher than, say, 0.05%). Such a definition excludes continuously variable characters such as height or skin colour in humans, but the human blood groups are classic examples, where single genes have two or more alleles, producing different antigenic phenotypes. A genetic polymorphism can be maintained by several mechanisms such as heterozygous advantage or FREQUENCY-DEPENDENT SELECTION, and can be stable over several generations (a BALANCED POLYMORPHISM) or may become ‘transient’ as when the environment changes; see, for example, SICKLE-CELL ANAEMIA. |