In a recent episode of the informative trivia series “Today I Found Out“, host and editor Daven Hiskey explains why both calico and tortoiseshell cats are almost exclusively female and how male exceptions can sometimes occur due to a specific chromosomal abnormality.
So, if a cat needs two X-chromosomes in order for its fur to be calico, how do male calico cats exist at all? A male cat can have tri-colored fur if he inherits an extra X-chromosome, making his genetic makeup XXY. In humans, this condition is known as Klinefelter Syndrome, which is surprisingly common at about 1-2 out of every 1000 live male births, with many who have the condition remaining ignorant of it. In humans, as with cats, the individual in question is usually considered genetically male despite having two X chromosomes. Besides potential other health issues, the extra X-chromosome almost always causes male calico or tortoiseshell cats to be sterile.