Two studies linking orange cat fur to a roughly 5 kb deletion in noncoding DNA near Arhgap36 on the X chromosome have received renewed attention. One study examined data from 188 cats and found the deletion in every orange cat tested, with thirteen-fold higher gene RNA expression in the relevant pigment cells. Random X-chromosome inactivation in females explains calico and tortoiseshell patterns. The studies were published in 2025. Stanford’s explanation also notes that expression differences were not found in non-skin tissues such as the brain, providing no basis for linking coat color to intelligence.