Isoform distributions. (A) Distributions of 16 possible isoforms in eight populations. Percentage of population accorded to each isoform is color coded. (B) Pairwise linkage between editing at the four sites is color coded as Lewontin's D' statistic, where +1 and −1 represent complete positive or negative coupling, and 0 represents independence. The starred squares indicate significant coupling (P < 0.02; Fisher's exact test).