The Hill-Robertson Effect and the Evolution of Recombination

• Published in: Genetics (Austin) Vol. 173; no. 3; pp. 1793 - 1811
• Main Authors: Roze, Denis, Barton, Nick H
• Format: Journal Article
• Language: English
• Published: United States Genetics Soc America 01.07.2006; Genetics Society of America; Copyright © 2006 by the Genetics Society of America
• Subjects: Alleles; Animals; Differences; Equilibrium; Evolution, Molecular; Gene loci; Genetic Drift; Genetic recombination; Humans; Investigations; Models, Genetic; Models, Statistical; Molecular biology; Mutation; Population; Probability; Recombination, Genetic
• ISSN: 0016-6731; 1943-2631; 1943-2631
• DOI: 10.1534/genetics.106.058586

In finite populations, genetic drift generates interference between selected loci, causing advantageous alleles to be found more often on different chromosomes than on the same chromosome, which reduces the rate of adaptation. This "Hill-Robertson effect" generates indirect selection to increase recombination rates. We present a new method to quantify the strength of this selection. Our model represents a new beneficial allele (A) entering a population as a single copy, while another beneficial allele (B) is sweeping at another locus. A third locus affects the recombination rate between selected loci. Using a branching process model, we calculate the probability distribution of the number of copies of A on the different genetic backgrounds, after it is established but while it is still rare. Then, we use a deterministic model to express the change in frequency of the recombination modifier, due to hitchhiking, as A goes to fixation. We show that this method can give good estimates of selection for recombination. Moreover, it shows that recombination is selected through two different effects: it increases the fixation probability of new alleles, and it accelerates selective sweeps. The relative importance of these two effects depends on the relative times of occurrence of the beneficial alleles.