Allele Frequency - The Effect of Mutation

The Effect of Mutation

Let ú be the mutation rate from allele A to some other allele a (the probability that a copy of gene A will become a during the DNA replication preceding meiosis). If is the frequency of the A allele in generation t, then is the frequency of the a allele in generation t, and if there are no other causes of gene frequency change (no natural selection, for example), then the change in allele frequency in one generation is

where is the frequency of the preceding generation. This tells us that the frequency of A decreases (and the frequency of a increases) by an amount that is proportional to the mutation rate ú and to the proportion p of all the genes that are still available to mutate. Thus gets smaller as the frequency of p itself decreases, because there are fewer and fewer A alleles to mutate into a alleles. We can make an approximation that, after n generations of mutation,