Influence of Sex on Selection I. Contribution of Sex-Linked Genes

Abstract

Consequences of individual selection and relaxation from selection are examined for genotypes generated by sex-linked genes. Two levels of complexity are studied. At the 1st level genotypes are derived from an arbitrary number of alleles at one locus. This situation is sufficiently general to include any pattern of dominance parameters. It is shown that the increment responses to selection for the 2 sexes may be different since they are different functions of genotypic variances and covariances. As a result of selection, the frequencies for the same allele diverge in the 2 sexes. Hence, on relaxation from selection, both male and female means fluctuate until gene equilibrium is reached. The 2nd level of complexity concerns populations generated by an arbitrary number of alleles at each of 2 sex-linked loci. This situation is generalized to include any pattern of dominance and epi-static effects. It is shown that the immediate responses to selection involve not only additive and additive X additive variances, as defined for both sexes, but also covariances for each class of these effects between sexes. Results from relaxation are complicated not only because of the fact that genes at both loci tend to equilibrate, but also because of the decay of the additive X additive epistatic contributions. Thus, at equilibrium only the additive genetic variances and covariances contribute to the permanent gain due to the past history of selection.