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In population genetics, the concept of effective population size ''N''''e'' was introduced by the American geneticist Sewall Wright. He defined it as "the number of breeding individuals in an idealised population that would show the same amount of dispersion of allele frequencies under random genetic drift or the same amount of inbreeding as the population under consideration". More generally, an effective population size may be defined as the number of individuals in an idealized population that has a value of any given population genetic quantity that is equal to the value of that quantity in the population of interest. The two population genetic quantities identified by Wright were the one-generation increase in variance across replicate populations (variance effective population size) and the one-generation change in the inbreeding coefficient (inbreeding effective population size). These two are closely linked, and derived from F-statistics, but they are not identical. Today, the effective population size is usually estimated empirically with respect to the sojourn or coalescence time, estimated as the within-species genetic diversity divided by the mutation rate. Another important effective population size is the selection effective population size 1/scritical, where scritical is the critical value of the selection coefficient at which selection becomes more important than genetic drift. However defined, the effective population size is usually less than the census population size (''N''). == Variance effective size == In the Wright-Fisher idealized population model, the conditional variance of the allele frequency , given the allele frequency in the previous generation, is : Let is defined as the size of an idealized population with the same variance. This is found by substituting and solving for which gives : 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「effective population size」の詳細全文を読む スポンサード リンク
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