Six relative rates. (A) Schematic of how fourfold synonymous sites were chosen: The center base of the triplet acquired a substitution on the D. melanogaster branch and is conserved in the rest of the Drosophila tree, and the outer bases of the triplet are conserved across the entire Drosophila tree. (B) Six relative rates within singletons (∼1(c)/621) calculated across different triplet contexts in nonrepetitive regions, and (C) six relative rates within substitutions at fourfold synonymous sites, calculated across different triplet contexts. Note that the six relative rates within C are significantly closer to the six relative rates within B than is expected by chance (P < 0.001), indicating that mutational patterns within rare polymorphisms have predictive power for evolution at synonymous sites.
