On the optimal sex ratio.
The equilibrium structures for various multiallele sex-determining genetic models of panmictic populations with sex expression depending on the genotypes of either the zygote or a parent are described. Even-sex-ratio equilibrium surfaces can exist apart from equilibrium points having coincident male and female allelic frequency sets. The latter (symmetric) equilibrium states entail biased sex ratios. A stable symmetric equilibrium and an even-sex-ratio equilibrium segregating the same alleles cannot coexist. The tendency to evolve toward an even-sex ratio is embodied by the following optimality property: starting from an equilibrium having a biased sex ratio, mutant sex-determining alleles can accumulate only in the case in which in the augmented system all attainable equilibrium states have a sex ratio closer to one to one.
D000483:Alleles; D000818:Animals; D005075:Biological Evolution; D005260:Female; D008297:Male; D008433:Mathematics; D008957:Models, Genetic; D010944:Plants / Q000235:genetics; D012732:Sex Determination Analysis; D012744:Sex Ratio; D013045:Species Specificity