FIG 1 .

Simulations of background selection without recombination. (A) Estimates of effective population size (N_e), as a function of actual population size (N). Note the log on the x axis. N_e was predicted theoretically by using the coalescent (28) or coarse-grained transformation to match smaller simulations (24). The coarse-grained approach was only possible for up to 2 × 10⁶ individuals. N_e was also estimated from simulations with 10⁶ to 10⁹ individuals, based on either the average diversity at a neutral site, π, or the frequency of deleterious background alleles, f_del. (B) The effectiveness of selection on a focal allele in the presence of background selection. The x axis shows the selection coefficient of the focal allele (note the log scale), and the y axis shows the average frequency of the deleterious allele at that site. The curve shows the theoretical expectation given N_e (as estimated using diversity at a neutral site). In both panels, the vertical bars show 95% confidence intervals.