Figure 2.

Distribution of K_s differences between duplicate genes for gene pairs with different amino-acid substitution rates. The x axis is the K_s difference between duplicate genes (the K_s of the fast-evolving copy minus the K_s of the slow-evolving one). The y axis is the number of gene pairs within a K_s bin. This figure shows that most pairs have a positive K_s difference, which suggests that the fast-evolving copy usually has a higher K_s than the slow-evolving copy.