Paper detail

The rate of adaptation in large sexual populations with linear chromosomes

In large populations, multiple beneficial mutations may be simultaneously spreading. In asexual populations, these mutations must either arise on the same background or compete against each other. In sexual populations, recombination can bring together beneficial alleles from different backgrounds, but tightly linked alleles may still greatly interfere with each other. We show for well-mixed populations that when this interference is strong, the genome can be seen as consisting of many effectively asexual stretches linked together. The rate at which beneficial alleles fix is thus roughly proportional to the rate of recombination, and depends only logarithmically on the mutation supply and the strength of selection. Our scaling arguments also allow to predict, with reasonable accuracy, the distribution of effects of fixed mutations when new mutations have broadly-distributed effects. We focus on the regime in which crossovers occur more frequently than beneficial mutations, as is likely to be the case for many natural populations.