Science Assessment

Dogs, pigs, and cats have similar genes for traits that they share in common (such as four legs, a tail, etc.) One of these genes, Gene X, is pictured below. 

Why do you think the DNA sequence of Gene X for dogs, pigs, and cats is the same at some of the positions (pictured in black)?

1. All three species inherited the gene from a common ancestor.
2. All three species had similar needs, so they had to intentionally create similar genes.
3. Separate mutations in the three species made the genes similar by coincidence.
4. Not enough information is given.