Figure P22.8. Timescale of change in the above example, with m = 0.002 (blue) or m = 0.0035 (red). For each migration rate, allele frequency p_A is shown falling from 1, and p_B increasing from 0. Thus, if m > 0.0025, the frequency of A^P decreases under the pressure of migration and eventually becomes so rare that allele B^P can increase: The population then fixes the opposite combination A^QB^P. (Black curves) Exact calculation, allowing for linkage disequilibrium: The discrepancy is not large, which justifies our approximation of ignoring linkage disequilibrium.

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