Fig. 2.

Frequency distributions of amino acid substitution rates (d _A) obtained from pairs of duplicate genes on duplicate blocks of the latest large-scale duplication (PPP1) in the rice genome. These distributions suggest another potential older large-scale duplication (PPP2). (a) A phylogenic tree with suspected two large-scale duplication events: PPP1 that predates the divergence of the cereals (Paterson et al., 2004) and PPP2 that predates monocot-dicot divergence (this study); (b) Frequency distributions of d _A values obtained from pairs of duplicate genes on duplicate blocks of PPP1; (c) Compositional analysis of (b). Pairs of duplicate genes of PPP1 were divided. In addition to the peaks in age distribution corresponding to PPP1, another obvious peak that suggests an older large-scale duplication (PPP2) was detected; (d) Frequency distributions of amino acid substitution rates obtained from pairs of duplicate genes among chromosomes (inter-chromosome) in the Arabidopsis genome. Pairs of duplicate genes were identified using the same method as in rice