More genes escape X inactivation in humans than in the mouse. Distribution of genes subject to X inactivation (blue) and of 'escape' genes (orange) in human and mouse. The position of the pseudoautosomal regions (PAR1 and 2 in human, PAR in mouse), of the centromeres (cen, purple bar), and of the X-inactivation center encoding the long noncoding RNA XIST/Xist (black bar) are indicated. Note that as the centromere is located at one end of the mouse X chromosome, there is no short arm or long arm. Data from Carrel and Willard  and Yang et al. .