Deleterious mutations as an evolutionary factor: 1. The advantage of recombination

Abstract

SUMMARYA population withudeleterious mutations per genome per generation is considered in which only those individuals that carry less than a critical number ofkmutations are viable. It has been shown previously that under such conditions sexual reproduction is advantageous. Here we consider selection at a locus that determines recombination frequency of the whole genome. The valuev=u/ √khas been found to play the decisive role. Whenv< 0·35 the direction of selection for recombination may be different for different cases, but the intensity of selection is always very small. The advantage of recombination becomes considerable whenv> 0·5, its growth under increasingvbeing approximately linear. Ifv> 2 no less than 95% of the progeny are bound to die because of the selection against deleterious mutations. Since this seems to be too great a mutation load, we may assume 0·5 < v < 2·0 for any sexual population if mutation really maintains crossing-over. Results on selection at a locus which controls mutability provide evidence thatvis located within the specified interval if the physiological cost of a twofold reduction of the mutation rate is within the range 10–80%. A number of consequences of this hypothesis about the mechanism of selection for sex and recombination are discussed.