Evolution: Snakes Have the Blueprints for Arms and Legs Still Encoded in Their Genome

Snakes may not have arms or legs, but they do have the blueprints for them in their genome. Scientists have found that embedded in snakes' genetic code was DNA that, in most animals, controls the development and growth of limbs.

Snakes weren't always legless; they evolved the loss of limbs over 100 million years ago. It would make sense that snakes would have the genetic blueprint for limbs. However, how did snakes manage to keep this blueprint for so many years after losing their limbs? Scientists may have the answer.

"There have been many millions of snake generations since they evolved a legless body, and we would generally expect the DNA associated with limb development to fade away or mutate to do another job, but that doesn't seem to have happened," said Douglas Menke, one of the researchers, in a news release. "Naturally, we wanted to know why snakes had retained DNA that they don't appear to need."

In this latest study, the researchers examined specific regions of noncoding DNA known as enhancers-a kind of switch that controls the expression of genes, telling them when to turn on or off during embryonic development. The scientists followed patterns of enhancer activity in embryonic limbs and genitalia of mice and lizards. This revealed that many of the same enhancers are activated during the formation of these different appendages in both species.

In fact, the researchers found that much of the genetic circuitry that controls the development of limbs is also important for the formation of genitalia. This may explain why snakes still have the genetic blueprints for limb development in their genome.

"We're only just beginning to understand the various roles of many of these enhancers," said Menke. "But what we generally refer to as 'limb enhancers' should probably be more broadly categorized as 'appendage enhancers,' because they clearly perform more than one job."

The findings are published in the journal Developmental Cell.

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