RBL subgroup evolved slightly slower than RB1 subgroup in vertebrates. (A) Distance between Human RB family proteins and predicted ancestral RB sequence. The pair wise distances between human RB1, RBL1, RBL2 and predicted ancestral RB sequence, RB-Mb (gi:167523296) sequence were computed. (B) Distance between human RB family proteins and their vertebrate orthologues. Pair wise distances were calculated between human RB1, RBL1, RBL2 and their orthologues in Gg, Xt, Dr, Tn, respectively. (C) The group average pairwise distances RB family in vertebrates. Based on protein sequences from 7 organisms (Hs, Mm, Cf, Bt, Rn, Gg, and Dr), the group average distance of RBL1 subgroup and RBL2 subgroup is smaller than RB1 subgroup (For RB1: RBL1, P < 0.001; RB1:RBL2, P < 0.001; with pair Student's T test), standard deviation values are showed as error bars. (D) Ka/Ks values for RB family genes deduced from sequences comparisons between human and other mammals. The ratio of nonsynonymous (Ka) to synonymous substitutions (Ks) of RB1, RBl1 RBL2 genes were computed, based on codoning sequences pairwise comparisons (Hs vs Mm, Hs vs Rn, hs vs Cf, hs vs Bt) respectively. (E) Average Ka/ks values for RB family gene in mammals. Based on the Ka/ks values for all protein-coding DNA sequences from 5 mammals (Hs, Cf, Bt, Mm, and Rn) in each subgroup, The group average Ka/ks value of RBL1 subgroup and RBL2 subgroup is smaller than RB1 subgroup with statistical support (For RBL1:RB1, P < 0.01; RBL2:RB1, P < 0.01), Detail information could be found in additional file 5 and additional file 6. Abbreviations used: Hs, H. sapiens; Mm, M. musculus; Cf, C. familiaris; Bt, B. Taurus; Gg, G. gallus; Xt, X tropicalis; Dr, D. rerio; Tn, T. nigroviridis; Ci, C. intestinalis; Sp, S. purpuratus; Bf, B. floridae.