News Genetics What gene makes orange cats orange? Scientists figured it out Calico and tortoiseshell cats also carry an X-chromosome mutation Orange fur in domestic cats usually arises from a specific DNA deletion in the X chromosome, two new studies suggest. Stefano Stefani/Getty Images By McKenzie Prillaman 7 hours ago Orange cats are so goofy that people joke that the chaotic kitties share one communal brain cell. But most of these domestic felines — along with multicolored calicos and tortoiseshells — actually do share something: a single genetic mutation that makes their fur ginger, researchers report in two studies published May 15 in Current Biology. The independent teams identified a DNA deletion that causes pigment cells to produce a yellow-red color rather than the default brown-black, solving a mystery that has stumped scientists for decades.  Sign up for our newsletter We summarize the week's scientific breakthroughs every Thursday.