Evolution of PAR genes in humans and mice. PAR genes that are downregulated in the ATRX-null mouse forebrain are clustered together within the PAR1 region of common evolutionary ancestors of humans and mice but have translocated to autosomes in the mouse. Vertical lines and arrows represent individual genes. The position of the first nucleotide of each gene is as follows: SHOX (505,079), CSF2RA (1,347,701), ASMTL (1,482,032), DHRSXY (2,147,553), CD99 (2,619,553), ARSD (2,848,421), ARSE (2,832,011) (Human reference sequence NCBI Build 36.1). PAR1, pseudoautosomal region 1; PAR2, pseudoautosomal region 2. PAR regions are highlighted in orange.