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Modern Genetic Analysis Chapter 17. Population and Evolutionary Genetics A Synthesis of Forces
Genetics In Process17-8: The balance between selection and mutation

If we let q be the frequency of the deleterious allele a and p=1q be the frequency of the normal allele, then the change in allelic frequency due to the mutation rate µ is

A simple way to express the fitness for a recessive deleterious gene is WA/A = WA/a = 1.0 Wa/a = 1 s, where s is the loss of fitness in homozygotes. We now can substitute these fitnesses in our general expression for allelic frequency change (see page 557) and obtain

Equilibrium means that the increase in the allelic frequency due to mutation must exactly balance the decrease in the allelic frequency due to selection, so

Remembering that

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