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The gamete column is what determines the frequencies of A and a that will be put into the gamete poo

The gamete column is what determines the frequencies of A and a that will be put into the gamete poo

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The gamete column is what determines the frequencies of A and a that will be put into the gamete pool for mating to build the next generation's genotypes. We can simplify by referring to the fitness of a genotype as w ii = m ii l ii . These fitness values will determine the contribution of that genotype to the next generation. Thus the frequency of A allele in the next generation p t+1 (sometimes referred to as p') would be the contributions from those genotypes carrying the A allele divided by all alleles contributed by all genotypes: p t+1 = (w AA p 2 + w Aa pq)/(w AA p 2 + w Aa 2pq + w aa q 2 ). Or for the a allele, q t+1 = (w aa q 2 + w Aa pq)/(w AA p 2 + w Aa 2pq + w aa q 2 ). Note that the heterozygotes are not 2pq but pq because in each case they are only being considered for the one allele in question. If we scale all wii's such that the largest = 1.0 we refer to these as the relative fitnesses of the genotypes. A worked example where p = .4, q = .6 and w AA = 1.0 w
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Unformatted text preview: Aa = 0.8 w aa = 0.6: Genotype frequencies are p 2 = 0.16, 2pq = 0.48, q 2 =0.36, thus: p t+1 = ((.16 x 1.0) + (.24 x .8))/((.16 x 1.0) + (.48 x .8) + (.36 x .6)) = .463; so q = .537 and thus f(AA) t+1 = .215, f(Aa) t+1 = .497 and f(aa) t+1 = .288. Note both allele frequencies and genotype frequencies have changed (compare to what we saw with inbreeding). This can be continued with the new allele frequencies and so on. When will the selection process stop? when ∆ p = 0, i.e., when p t+1 = p t . In some situations this will stop only when one allele is selected out of the population (p = 1.0). Now we can consider various regimes of selection (s = selection coefficient , (1-s) is fitness ): AA Aa aa I 1 1 1 - s selection against recessive II 1 - s 1 - s 1 selection against dominant III 1 1 - hs 1 - s incomplete dominance (0<h<1) IV 1 - s 1 1 - t selection for heterozygotes...
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