The leads to FST = 1.0 on the left where there is maximum variance in allele frequencies among the subpopulations given the allele frequencies, and FST = 0.0 on the right where there is no variance in allele frequencies among the subpopulations. Measuring the variance in allele frequencies among subpopulations is the basis of several widely employed methods used to estimate FST from actual genetic marker data (see Method box 4.2).

The relationship between the allele frequencies of subpopulations, the hierarchical measures of heterozygosity, and the fixation indices can be seen in a simulation of gene flow and genetic drift in a subdivided population (Fig. 4.8). When gene flow is relatively strong and maintains similar allele frequencies in the subpopulations, the expected heterozygosity of the subpopulations and the total population are also similar and result in low values of the fixation indices (Fig. 4.8a). When gene flow is weaker and the

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