Shifts in the intensity of purifying selection: An analysis of genome-wide polymorphism data from two closely related yeast species

The relationship between the intensity of purifying selection and the effective population size. The intensity of purifying selection is measured as the genome-wide estimate of f_π; the two proxies used for the effective population size are the genome-wide average synonymous heterozygosity values, (A) and (B), where is the average synonymous divergence (see text). Central 95th percentiles for the estimates, represented by the horizontal and vertical bars, were estimated by bootstrapping over genes. The dashed line in B shows the expected relationship between f and assuming a gamma-shaped distribution of mutational selective effects with a point mass at s = −∞ (see text and Methods). (C) Using the same distribution, the estimated fractions of effectively neutral, weakly deleterious, and strongly deleterious amino acid mutations in each population.