EVOLUTION OF THE SRY GENES

Existing DNA sequence data on the Sry gene, the mammalian sex-determin ing locus in the Y chromosome, were analyzed for primates, rodents, an d bovids. In all three taxonomic groups, the terminal sequences evolve d faster than the HMG (high mobility group) boxes, and this applies bo th to synonymous (K-s) and nonsynonymous (K-a) nucleotide substitution s. Similar intragenic correlation between synonymous and nonsynonymous substitution rates was not found either in other mammalian genes that contain a conservative box (Sox, Msx) or in the MADS-box genes of pla nts. The rate of nonsynonymous substitutions exceeds significantly tha t of synonymous substitutions in the terminal Sry sequences of apes. W e did not find good support for the hypothesis that the high evolution ary rate of Sry would be associated with a promiscuous mating system.