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Figure 4.14 Allele frequency in the two-island model of gene flow for a diallelic locus. Dashed lines in each panel highlight gene-flow-weighted average or equilibrium allele frequencies. Starting from allele frequencies of 0.9 and 0.2 and with equal rates of gene flow (m = 0.1), the subpopulations approach an equilibrium allele frequency ofp = (0.9 + 0.2)/2 = 0.55 (left panel). With initial allele frequencies of 0.9 and 0.2 but asymmetric rates of gene flow (m1 = 0.1 and m2 = 0.05), the subpopulations approach an equilibrium allele frequency ofp = (0.9 x 0.05 + 0.2 x 0.1)/0.15 = 0.433 (right panel). Equilibrium is reached more slowly in the case of asymmetric rates of gene flow on the right because the average rate of gene flow is lower. Note that the time scales in the two graphs differ.

is also longer when the migration rates are asymmetric. Consider the example where migration rates are unequal (m1 = 0.01 and m2 = 0.1) and the initial allele frequencies in the two subpopulations are p1 = 0.9 and p2 = 0.1. The weighted average allele frequency

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