Snakes Used to Have Legs, Biologists Reveal

The ancestors of the present day's slithery snakes used to have full-fledged arms and legs; however, genetic mutations led the reptiles to lose all their limbs approximately 150 million years back based on two new studies, reports National Geographic. The discoveries are great news for herpetologists, who have wondered for a long time on what genetic alterations led snakes to lose their limbs, said the researchers. Both the studies indicated that the DNA, popularly known as the Zone of Polarizing Activity Regulatory Sequence (ZRS), was basically responsible for the change.

The two teams used different methods to arrive at their findings. In one study, researchers took numerous mouse embryos and replaced their ZRS DNA with those of snakes. It was noted that the mice hardly grew any limbs instead of normal limb growth, pointing out to the fact that ZRS is important for the development of limbs, according to the team. This DNA is one of the main components required for the development of limbs in human beings as well as other legged vertebrates, said Axel Visel, senior author of the study and geneticist at California-based Lawrence Berkeley National Laboratory.

In the second study, researchers used a DNA-editing method known as clustered regularly interspaced short palindromic repeats (CRISPR). This method involved cutting out the ZRS stretch in the embryos of mice and replacing them with those of other animals and even snakes. It was seen that the mice developed normal limbs when they had ZRS DNA from humans and other animals. However, when the ZRS from cobra and python were inserted into the mice, their limbs barely developed. What this indicates is that it's possible for today's snakes to grow legs without taking an entire evolutionary cycle to achieve the feat, said Martin J. Cohn, biologist at University of Florida.

The findings were published in the journal Cell.