FIGURE 4. Gene family evolution. (a) The proportion of various gene classes among nine species. (b) Expansion and contraction of gene families in nine species. A phylogenetic tree was constructed based on 523 single-copy orthologous genes using O. sativa as the outgroup. Pie diagrams on each branch of the tree represent the proportion of genes undergoing gain (green) or loss (red) events, the numbers near the nodes represent number of gene families expanded or contracted. The scale on the X axis shows the estimated divergence time for nodes.