Polydactyly in humans

This person has six fingers on each hand and seven toes on each foot owing to a regulatory mutation in the Sonic hedgehog gene.

[Courtesy of Dr. Robert Hill, MRC Human Genetics Unit, Edinburgh, Scotland; from L. A. Lettice et al., “Disruption of a Long-Range Cis-Acting Regulator for Shh Causes Preaxial Polydactyly,” Proc. Natl. Acad. Sci. USA 99, 2002, 7548 © 2002 National Academy of Sciences, USA.]