In our metapopulation example above, on the left all demes have p = 0.5 and the allele frequency for the entire array is also p = 0.5. Right away you can se that there in no differentiation amongdemes. To quantify this we use Fst which is calculated as Fst = (Ht - meanHs) / Ht, where Ht = 2 (pooled p) (pooled q) [note that pooled q = (1-pooled p)], and meanHs = the average of H values for each of the individual demes (i.e., 2 p q for each deme, averaged across all demes). For the left-hand metapopulation Ht = 2(0.5)(0.5) = 0.5, and meanHs = 0.5 also. Thus , Fst = (0.5 - 0.5) / 0.5 = 0.0. What does this mean? In English this says that noneof the variation in this system of demes lies betweendemes; the population structure is zero. Since there is variation (i.e., p _ 0) allof the variation lies withindemes.Now consider the metapopulation system on the right above. The pooledallele frequency is 0.5 because half of the demes are fixed for the A allele (p = 1.0) and half are fixed for the a allele (p = 0.0). Hence the Ht value is 2 (pooled p) (pooled q) = 2(0.5)(0.5) = 0.5. The meanHs value is very different. Each deme has a heterozygosity
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