The rate of adaptation in large sexual populations with linear chromosomes

TL;DR

This paper investigates how beneficial mutations spread in large sexual populations with linear chromosomes, revealing that interference among linked alleles influences the fixation rate and depends on recombination frequency.

Contribution

It introduces a model showing that the genome acts as linked asexual segments under strong interference, with fixation rates scaling with recombination and mutation effects.

Findings

Fixation rate proportional to recombination rate

Genome behaves as linked asexual segments under interference

Distribution of fixed mutation effects can be predicted

Abstract

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.