Biology graduate student, Francisca Leal, and Professor Marty Cohn published an important new paper in Current Biology, “Loss and re-emergence of legs in snakes by modular evolution of sonic hedgehog and HOXD enhancers” (DOI: http://dx.doi.org/10.1016/j.cub.2016.09.020 ).
They show that hind limb development in python embryos is arrested due to mutations that abolish an essential transcription factor of Sonic hedgehog (SHH). This loss in snakes leads to the early termination of the genetic circuit that drives limb growth in lizards and other vertebrates with legs. The paper was described in the News section of Science: Tiny tweaks made snakes legless:
It was also described on NPR’s “Must Reads” with a video of Dr. Cohn describing the research: http://www.npr.org/sections/thetwo-way/2016/10/20/498575639/how-snakes-lost-their-legs