All animals with eyes or eyespots that have been studied so far share a gene in common. When mutated, the gene Pax-6 causes lack of eyes in fruit flies, tiny eyes in mice, and missing irises (and other eye parts) in humans. The sequence of Pax-6 in humans and mice is identical. There are so few sequence differences with fruit fly Pax-6 that the human/mouse version can cause eye formation in eyeless fruit flies, even though vertebrates and invertebrates last shared a common ancestor more than five hundred million years ago. The appearance of Pax-6 in all animals with eyes can be explained in multiple ways. Based on the information above, which explanation is most likely? a. Pax-6 in all of these animals is not homologous; it arose independently in many different animal phyla due to intense selective pressure favoring vision.
b. The Pax-6 gene is really not one gene. It is many different genes that, over evolutionary time and due to convergence, have come to have a similar nucleotide sequence and function.
c. The Pax-6 gene was an adaptation of an ancestral animal of the early Cambrium period. Animals with eyes or eyespots are descendants of this ancestor
d. The need for eyes has resulted in the separate evolution of Pax-6 genes