Dictionary of Human Evolution and Biology

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Balanced Polymorphism

State in which a population is usually maintained at equilibrium values by a selective superiority of the heterozygote over either class of homozygote. Characterized by changes in genotype frequencies due to selection against both homozygote classes but does not result in changes in allele frequencies between generations. One of the alleles is usually deleterious in the recessive homozygous genotype, as in sickle cell anemia. Rarely, this state is also achieved by selective superiority of both homozygote classes.

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