Dictionary of Human Evolution and Biology

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Genetic Drift

Change in allele frequency that occurs
(1) when small groups of individuals are separated from or leave a larger population (founder effect), or
(2) when offspring differ genetically from the parental population due to sampling error. Any differentiation of a small isolated population due to the fact that, by chance alone, its founders contained a set of allele frequencies with values different from those of other populations, and hence have drifted from the other population values; usually referred to in the diachronic sense, i.e. between generations. Drift is a possibly non-adaptive mechanism of evolution and is significant in diploid organisms when the effective population size (Ne) falls below about 30 sexually mature individuals. Aka the Sewell Wright effect.

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