Evolution of the Zfx and Zfy genes: rates and interdependence between the genes

A phylogenetic analysis of sex-chromosomal zinc-finger genes (Zfx and Zfy)indicates that the genes have not evolved completely independently sincetheir initial separation. The sequence similarities suggest gene conversionin the last exon between the duplicated Y-chromosomal genes Zfy-1 and Zfy-2in the mouse. There are also indications of conversion (or recombination)between the X- and Y-chromosomal genes in the crab- eating fox and in themouse. The method for estimating synonymous and nonsynonymous substitutionsis modified by incorporating the substitutions in the twofold-degeneratesites in a novel way. The estimates of synonymous substitutions support thegeneration-time hypothesis in that the obtained rates are higher in mice(by a factor of 4.7) than in humans and higher in the Y-chromosomal genes(by a factor of 1.9) than in the X-chromosomal genes.