Plot of expression level of mRNA in testes associated with each RP protein versus the number of processed pseudogenes associated with it. The top and bottom panels correspond to human and mouse RP pseudogenes, respectively. The x-axis shows signal on the gene chip, which is a measure of the abundance of a mRNA transcript. Data for the human and mouse are not normalized to each other and should not be compared directly. It should be noted that expression data for some RP proteins for mouse are missing in the GEO data.