since this rate is enough to balance the expected rate

of loss of heterozygosity by genetic drift 1 -

in an isolated population (see section 3.4).

The expected relationship between the fixation index and the effective number of migrants relies on the infinite island model for two reasons. First, in the island model all subpopulations have an identical rate of migration from all other populations so there is only a single migration rate (m) that applies to all subpopulations. Second, since there are an infinite number of subpopulations the entire ensemble population will never reach fixation or loss due to genetic drift. In an island model of gene flow where the number of subpopulations is finite, called the finite island model, the entire set of populations will eventually reach fixation or loss and FST will eventually decline to zero since the entire set of subpopulations will eventually reach fixation or loss due to genetic drift (Nei et al. 1977; Varvio et al. 1986). The expected amount of genetic differentiation in the finite island model is

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