Appendix 2—figure 1. While directional selection during the rapid phase increases the frequency of aligned alleles relative to opposing ones, the frequency of aligned alleles does not necessarily increase.

Here, we show an example of the trajectories of (A) moderate and (B) large effect alleles in response to a relatively small shift in optimum; the trajectories were calculated using Equations A3-39, A3-40 and A3-48 in Appendix 3. When directional selection is sufficiently weak (the shift is small), the frequency of aligned alleles with sufficiently large effects will decrease (B). However, the frequency of opposing alleles decreases more, and the frequency difference (in red) contributes to the change in mean phenotype.