Science Buddies: X Inactivation Marks the Spot for Cat Coat Color

A tortoiseshell cat has two different fur colors, black or brown and red or orange. The gene that gives rise to the red or orange fur color is on the X chromosome. Female cats have two X chromosomes, while males only have one, which allows the females to express two different color combinations; therefore, most tortoiseshell cats are female. Try this science fair project to figure out how female cats cope with having two X chromosomes, and if X chromosomes are inactivated in a random or in an allele-dependent manner.