BIOB51H3 Lecture Notes - Lecture 11: Frequency-Dependent Selection, Allele Frequency, Negative Frequency
20 Mar 2019
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Pattern of selection: negative frequency-dependent selection, heterozygote superiority, one allele favoured, heterozygote inferiority, mutation-selection balance. When the fitnesses of two alleles are equal means equal lifetime reproductive success. Leads to balanced polymorphism: stable equilibrium with more than one allele: heterozygote advantage/ overdominance. See figure 7. 14: heterozygotes = highest fitness, clue: allele freq. often at stable equilibrium, clue: heterozygotes at higher frequency than expected under h-w. Because you are having simultaneous selection for both of those alleles through the heterozygous form. Leads to balanced polymorphism: stable equilibrium with more than one allele: one allele favoured (directional selection) See figure 7. 13: often leads to fixation of favoured allele and loss of other allele, an allele is fixed when its freq. = 1. 0: an allele is lost when its frequency = 0. 0 (no longer present in the population) rate of change depends on: initial frequency of each allele, dominance, see figure 7. 13 b. Directional selection reduces genetic diversity: heterozygote inferiority (underdominance)
