equation 4.50 the e 2Ne term gets smaller as time increases. This serves to approximate what happens to Fst as t increases: the average expected heterozygosity of subpopulations (HS) decreases and eventually reaches zero, with the consequence that FST reaches 1. This results from the process of genetic drift, causing all subpopulations to eventually reach fixation or loss. Note, however, that the total population heterozygosity (HT) is not impacted by genetic drift since each subpopulation has equal chances of fixation or loss and there are an infinite number of subpopulations.

Next we will move on to consider what occurs in the infinite island model when both gene flow and genetic drift are acting at the same time. In Chapter 3, the fixation index:

t 2N

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