Fig. 2.

Average beneficial allele frequency (long-term average) for a single-locus model, under the general model (SI Appendix, Eq. S2, solid lines), the infinite population size model (SI Appendix, Eqs. S3a and S3b, short-dashed lines), and the sequential-fixation model (Eq. 1, long-dashed lines). Results from Wright–Fisher simulations are given as solid points for the case in which the actual and effective population sizes are equal ($N_e=N=\mathrm{1,000}$). The mutation rate of beneficial to deleterious alleles ($u_{10}$) is three times the reciprocal rate (as would be the approximate case for a single optimal nucleotide at a site). The infinite population size results use the selection coefficient inferred by the constant product $Ns$ for each curve, so that $s$ in this case scales inversely with $N$.