Proposed model for the co-regulation of ancestral PAR genes by ATRX. Mice and humans diverged from a common ancestor approximately 50 million years ago. In humans, genes have remained in the PAR region (orange) while in mice and rats they have translocated to autosomes (grey). Our data suggest that despite the translocation of these genes to autosomes (numbered), they still share a common sequence or chromatin environment that allows ATRX (green circles) to keep these genes active. We propose that this common feature was conserved upon translocation from the pseudoautosomal region on the X and Y chromosomes in the ancestral PAR to their current autosomal locations in the mouse genome. mya, millions of years ago.