Effects of selection and drift on the dynamics of finite populations

Abstract

Selection, in the case of a variable finite population size and a two-allelic locus with overdominance, caused an acceleration in the time to fixation or loss of the favorable allele (i.e. time with selection was less than that with no selection) when the deterministic gene frequency equilibrium was above 0.8. The acceleration was over a range of initial gene frequencies, dependent on the selection intensity and the overdominance parameter.In the case of multiple loci and a small, diploid population of fixed size derived from a large population in initial linkage equilibrium, an acceleration in the time to fixation or loss occurred over a range of initial gene frequencies (as in the one locus case) for strong selection intensity (N s>14) and weak overdominance effect. For a large number of overdominant loci, acceleration did not occur under linkage. Initial coupling or repulsion disequilibrium with independent assortment had no effect on the observed acceleration. Repulsion with linkage, however, caused a retardation in the time to fixation or loss.