The relationship between nonsynonymous rate (K_A) and the transformed correlation coefficient of gene expression values between duplicate genes: 60 gene pairs with K_A < 0.2 from group A (A); 153 gene pairs with K_A < 0.2 from group B (B); 165 gene pairs with 0.2 < K_A < 0.7 from group A (C); and 609 gene pairs with 0.2 < K_A < 0.7 from group B (D).