Effect of drift, selection and recombination on the equilibrium frequency of deleterious mutations

TL;DR

This paper analyzes how genetic drift, selection, and recombination influence the equilibrium frequency of deleterious mutations in populations, providing exact calculations and bounds for different population scenarios.

Contribution

It offers exact solutions and bounds for the steady state frequency of deleterious mutations considering various population sizes and recombination effects.

Findings

Deleterious mutation fraction decreases with increasing population size.

Recombination reduces deleterious mutations more effectively in moderately large populations.

Recombination has a significant impact when beneficial mutations are rare.

Abstract

We study the stationary state of a population evolving under the action of random genetic drift, selection and recombination in which both deleterious and reverse beneficial mutations can occur. We find that the equilibrium fraction of deleterious mutations decreases as the population size is increased. We calculate exactly the steady state frequency in a nonrecombining population when population size is infinite and for a neutral finite population, and obtain bounds on the fraction of deleterious mutations. We also find that for small and very large populations, the number of deleterious mutations depends weakly on recombination, but for moderately large populations, recombination alleviates the effect of deleterious mutations. An analytical argument shows that recombination decreases disadvantageous mutations appreciably when beneficial mutations are rare as is the case in adapting microbial populations, whereas it has a moderate effect on codon bias where the mutation rates between the preferred and unpreferred codons are comparable.