Figure 2.

The mean number of nonsynonymous substitutions at the PBR among HLA-DRB1 allele pairs that share the same coalescence time. The ordinate axis represents the mean number of nonsynonymous substitutions at the PBR among allele pairs [K_B(m)]. The abscissa axis represents the number of substitutions at putative neutral sites (m = K_S + K_N). The Roman numerals indicate the four phases that are classified as per variation in patterns of K_B(m) values (see text). Error bars indicate the SD from the mean.