The probability that a nonsynonymous SNP is functional is computed with the program SIFT, which considers the extent to which any polymorphic site is evolutionarily conserved across all good homologs in the public databases. Because only half of the nonsynonymous SNPs are SIFT analyzable, bin 1 is unchanged from Fig. 1, but bins 2 + 3 and 4 + 5 are merged together to improve statistics. Of these 154 analyzed SNPs, only 55 are predicted to be functional.