Research overview: polydactyly in cats, history and genetics

Polydactyly, the presence of extra toes, is a common congenital trait in cats caused by dominant mutations in a limb-development regulatory region near the Sonic hedgehog gene. This overview surveys the genetics, geography and folklore of polydactyl cats, which are notably frequent in parts of England, the eastern United States and maritime communities, consistent with spread along shipping routes where sailors prized them. It covers the molecular basis of the preaxial polydactyly that produces mitten-like paws, the generally benign nature of the trait, and rarer complex forms linked to limb deformity. The famous colony at Ernest Hemingway's Florida home illustrates how founder effects and human preference maintain visible pockets of high polydactyly frequency.