Pseudogene ages. Top three panels: Distributions of GAPDH pseudogenes by age in the human, mouse, and rat genomes. There appear to be three distinct bursts in retrotransposition which gave rise to GAPDH pseudogenes centered around medians (middle 50%) of 42.0 million years ago (26.4-49.3 million years) in human, 36.3 million years ago (17.4-52.8 million years) in mouse, and 25.9 million years ago (17.6-40.9 million years) in rat. Pairwise Kolmogorov-Smirnov testing shows that the age distributions among these three genomes are statistically different, with p-values of 0.01 (human-mouse), 7 × 10-7 (human-rat), and 7 × 10-10 (mouse-rat). Bottom two panels: Distributions of GAPDH pseudogenes syntenic between mouse and rat. Although the majority did occur before the mouse-rat divergence 41 million years ago, there is some noise or variation in nucleotide substitutions.