Base your answers to questions 69 through 72 on the information below and on your knowledge of biology.
Snakes Used to Have Legs and Arms Until These Mutations Happened
The ancestors of today’s slithery snakes once sported full-fl edged arms and legs, but genetic mutations caused the reptiles to lose all four of their limbs about 150 million years ago, according to two new studies. …
Both studies showed that mutations in a stretch of snake DNA called ZRS (the Zone of Polarizing Activity Regulatory Sequence) were responsible for the limb-altering change. But the two research teams used different techniques to arrive at their findings. …
…According to one study, published online today (Oct. 20, 2016) in the journal Cell, the snake’s ZRS anomalies [differences] became apparent to researchers after they took several mouse embryos, removed the mice’s ZRS DNA, and replaced it with the ZRS section from snakes. …
…The swap had severe consequences for the mice. Instead of developing regular limbs, the mice barely grew any limbs at all, indicating that ZRS is crucial for the development of limbs, the researchers said.
Looking deeper at the snakes’ DNA, the researchers found that a deletion of 17 base pairs within the snakes’ DNA appeared to be the reason for the loss of limbs.
Source: http://www.livescience.com/56573-mutation-caused-snakes-to-lose-legs.htm