The evolution of the Y chromosome with X-Y recombination
Clark, A.G.
Genetics 119(3): 711-720
1988
ISSN/ISBN: 0016-6731 PMID: 3402733 Document Number: 308164
A theoretical population genetic model was developed to explore the consequences of X-Y recombination in the evolution of sex chromosome polymorphism. The model incorporates 1 sex-determining locus and 1 locus subject to natural selection. Both loci have 2 alleles, and the rate of classical meiotic recombination between the loci is r. The alleles at the sex-determining locus specify whether the chromosome is X or Y, and the alleles at the selected locus are arbitrarily labelled A and a. Natural selection is modelled as a process of differential viabilities. The system can be expressed in terms of 3 recurrence equations, 1 for the frequency of A on the X-bearing gametes produced by femalefemale and 1 for each of the frequencies of A on the X- and Y-bearing gametes produced by malemale. Several special cases were examined, including X-chromosome dominance and symmetric selection. Unusual equilibria were found, the 2 sexes having very different allele frequencies at the selected locus. A significant finding was that allowing recombination resulted in a much greater opportunity for polymorphism of the Y-chromosome. Tighter linkage resulted in a greater likelihood for equilibria, with a large difference between the sex chromosomes in allele frequency.