Figure 3

Comparison of duplication age distributions between different groups of genes. The x-axis was the evolutionary age (from now) in million years. The y-axis was the density of the distributions. A) GPCRs vs. the "downstream genes"; B) GPCRs vs. G Proteins; C) Between different subclasses of GPCRs (The densities was multiplied by the number of genes in correspondent subclasses to reflect the differences in frequencies); D) GPCRs with peptide-ligands vs. non-peptide ligands.