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Unformatted text preview: 1/18/10 1 128 128 A simple model of mutation-selection equilibrium Two alleles: wild-type allele, A, at freq = p deleterious allele, a at freq = q Assume the mutation rate to recessive deleterious alleles, A to a = , and that back mutation is rare and can be ignored Recall that the spread of a dominant, beneFcial allele is described by the equation p = spq 2 /w Bar (see earlier slide) This implies that a recessive deleterious allele is removed at rate q = -spq 2 /w With only two alleles, any increase of the beneFcial allele is at the expense of the deleterious allele! Mutation-selection equilibrium occurs when: spq 2 / w Bar = p If the deleterious allele is rare then w Bar , which is 1-sq 2 , is 1 because q 2 0 Then, spq 2 = p, and sq 2 = . inally, q 2 = /s, and q = /s 129 129 If a deleterious allele is not completely recessive, then: q = /hs, where h and s are the dominance and selection coeff. A small amount of dominance has a large effect on decreasing q, the frequency of the deleterious allele at equilibrium....
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- Winter '10