Equilibrium allele frequencies in terms of invasion and fixation conditions
Joint work with Matthew Osmond.
Genetic variation can be maintained by balancing selection. This requires that an allele
invades' (increases in frequency when rare) but does not˝x' (declines near 100% fre-quency). Balancing selection pushes these alleles towards an intermediate `equilibrium' frequency. Here, we use a general formulation to show that the equilibrium frequency can often be written as a simple ratio of the conditions for invasion and ˝xation. This rela-tionship requires that marginal ˝tness increases linearly with allele frequency, a common assumption in population genetic models. We therefore connect many models in the same framework and provide a concise and interpretable expression for equilibrium frequency.