The null hypothesis of evolution. Without selection, allele frequencies never change — so watch what happens when you give the genotypes different fitness.
Hardy-Weinberg & SelectionLive
population genetics
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Without selection, allele frequencies stay put and genotypes settle at p², 2pq, q² — Hardy-Weinberg equilibrium. Give the genotypes different fitness and selection shifts the allele frequency each generation. Heterozygote advantage (high Aa fitness) can hold both alleles in a stable balance.
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How it works
Hardy-Weinberg equilibrium predicts stable genotype frequencies p², 2pq, q² in the absence of evolutionary forces. Introducing fitness differences lets selection shift the allele frequency each generation, driving one allele to fixation, to loss, or — with heterozygote advantage — to a stable polymorphism. The foundation of population genetics.
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