DYNAMICS OF POLYGENIC VARIABILITY UNDER STABILIZING SELECTION, RECOMBINATION, AND DRIFT

We study the transient dynamics of the genotypic variance of an additi ve trait under stabilizing selection, recombination and random drift. We show how interaction of these factors determines the form and the r ates of change of different components of the genotypic variance. Let V-g be the genic variance of the trait and C-L be the contribution of linkage disequilibrium to the genotypic variance. We demonstrate that the dynamics of the system on the plane (V-g, C-L) are typically chara cterized by a quick approach to a straight line with slow evolution al ong this line afterwards. We show that the number of loci, n, and the population size, N, affect the expected dynamics of V-g mainly through the ratio N/n. We use our analytical and numerical results in interpr eting the published results of artificial stabilizing selection experi ments. The analysis suggests that it is drift and not selection that m ost likely led to the reduction of genetic variability in most of thes e experiments. Even very strong stabilizing selection only slowly remo ves polygenic variability from populations.