Evolutionary analysis of proteins involved in synaptic transmission. (a) The empirical cumulative distribution of protein evolutionary rate, measured by dN/dS, was calculated for human-mouse orthologs. Data for 139 human-mouse orthologs of mainly presynaptic genes is shown in red whereas a comprehensive survey of more than 15,000 homologous pairs of human-mouse orthologs is shown in black. (b) The distribution of dN/dS calculated for human-mouse orthologs was grouped by gene family. All family members are shown in red and extreme members outside whiskers are labeled. Black boxes showing the 25% quantile, the median, and 75% quantile are superimposed, and whiskers extend to the most extreme data point that is no more than the interquartile range in both directions from the median in the box. (c) The distribution of dN/dS calculated for human-rat orthologs was grouped by gene family. (d) The distribution of dN/dS calculated for mouse-rat orthologs grouped by gene family. dN, nonsynonymous rate of change; dS, synonymous rate of change.