Comparison of random monoallelic expression in human and mouse genomes. (a) Human and mouse random monoallelic expression (RMAE). Of all orthologous gene pairs between mouse and human, there were 529 for which the gene was assessed (as either biallelic expression, RMAE class I or RMAE class II) in each organism. Of these orthologs, 66 were RMAE in mouse and 29 were RMAE in human, resulting in a subset of 15 genes that were assessed as RMAE in both organisms. (b) The number of assessed orthologs showing RMAE in both species is greater than would be expected by chance (Note 6 in Additional file 1). The observed and expected overlaps are shown as subsets of the gray bars, which represent the maximum possible overlap, as defined by the total number of RMAE genes (29) observed in human (for an overlap of 15 or more genes; hypergeometric P < 2 × 10-7).