Dorking's fifth toe in developmental research

A 2009 study examined how Dorking embryos form an extra digit on the inner side of the foot. The researchers investigated signaling during limb formation and found unusual expression of several developmental genes, including FGF4 and Sonic Hedgehog. They also observed reduced programmed cell death in part of the developing limb.

Their experiments indicated that the FGF-related changes could begin independently of the unusual Sonic Hedgehog expression. This is an important correction to the idea that every five-toed chicken must acquire the feature through exactly the same molecular route. An extra toe is a shared visible outcome, while different populations can provide different developmental models. The study explains Dorking limb development; it is not a reconstruction of Roman ancestry or proof that any five-toed farm chicken belongs to the breed.