Interact box Twoisland model of gene flow

The two-island model of gene flow can be simulated in PopGene.S2. Launch PopGene.S2 and select Island-island model of migration from the Gene Flow and Subdivision menu. The simulation window has entry fields to set initial allele frequencies in each island subpopulation, the rate at which each island receives immigrants from the other island, and the number of generations to run the simulation. Enter parameters of pi = 0.9, p2 = 0.1, ml = 0.1, m2 = 0.1, and 100 generations to run. Before clicking the OK button, predict the equilibrium allele frequency in each subpopulation.

A major conclusion from the two-island model is that the allele frequencies in each subpopulation approach the average allele frequency in the total population. Confirm that equal migration rates for both subpopulations give an equilibrium allele frequency of the average of the initial allele frequencies (for example, try pi = 0.6, p2 = 0.4, mi = 0.1, and m2 = 0.1, and then pi = 0.99, p2 = 0.01, mi = 0.1, m2 = 0.1). Also simulate cases when the migration rates are not equal (such as pi = 0.9, p2 = 0.1, mi = 0.01, m2 = 0.1) and use the the gene-flow-weighted average of the allele frequencies to predict allele frequencies at equilibrium.

Let's first consider what will happen in the infinite island model when there is no gene flow among the subpopulations (m = 0). Since each subpopulation is a finite island, allele frequencies will vary from one generation to the next simply due to genetic drift. The expected value of the fixation index for subpopulations compared to the total population is:

fst 1 e

where t is time in generations and Ne is the effective size of a single subpopulation (Wright 1943a). In

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