Polydactyly – having more than five fingers or toes – is surprisingly common in the population, with roughly one in 500 children born with extra digits. It's due to faulty patterns of gene activity as a baby's limbs are developing in the womb, and scientists are trying to track down the culprits. Mice develop paws in the same way we build our hands and feet, so they're a good model for figuring out what's going on. The bones on the left are from the hind foot of a normal mouse with five toes. But the foot on the right belongs to an animal with a faulty version of a gene called Gata6, resulting in seven toes. Unravelling the complex genetic network that creates the correct number of fingers and toes in mice is shedding light on what goes on during the development of our own hands and feet.
Written by Kat Arney