Base your answers to questions 1 through 4 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-fledged 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.

1. Without having DNA samples from snakes 150 million years ago, state how scientists could
know that snakes once actually had legs.

Scientists can infer that snakes once had legs through a variety of methods, despite not having direct DNA samples from snakes 150 million years ago.

One approach is to study the fossil record. Fossils of ancient snake relatives, such as primitive snakes like Najash rionegrina and Pachyrhachis problematicus, have been discovered with well-preserved limb bones. These fossils exhibit clear evidence of reduced but functional limbs, providing a link between snakes and their legged ancestors.

Comparative anatomy is another powerful tool. By examining the anatomy of modern snakes, scientists can identify vestigial structures, such as pelvic spurs and remnants of hind limb bones, which are remnants of their legged past. These structures serve no functional purpose in snakes but are homologous to the limbs of other reptiles.

Additionally, developmental biology studies contribute to our understanding. Embryological studies of snakes have shown that during early stages of development, snake embryos display limb buds similar to other reptiles.

However, these limb buds regress and do not fully develop. By comparing this process with other reptiles' limb development, scientists can deduce that snakes have a genetic program for limb development that has been modified over time.

Combining evidence from fossils, comparative anatomy, and developmental biology, scientists can confidently conclude that snakes once possessed legs and subsequently underwent evolutionary changes resulting in the loss of their limbs around 150 million years ago.

Know more about fossils here:

https://brainly.com/question/14477894

#SPJ8