P

= 0.00

identical in state are always identical by descent. If the infinite alleles model is not met, D underestimates the true genetic distance because the mutational events that record the history of the populations will not be reflected perfectly in the allele frequencies.

With an awareness of mutation models, we can also reflect back on measures of genetic divergence among populations covered earlier in the book. Chapter 4 gave the expression for the fixation index among subpopulations relative to the total population H _h

^ P ' It turns out that this assumes the

H„, infinite alleles model since it treats all alleles as being an equal number of mutational steps apart with all heterozygotes considered equally distant. There is an alternative method to compute the fixation index that depends instead on the stepwise mutation model where the fixation index is measured by

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