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 500 million years ago.
-Fruit fly eyes are of the compound type, which is structurally very different from the camera-type eyes of mammals. Even the camera-type eyes of molluscs, such as octopi, are structurally quite different from those of mammals. Yet, fruit flies, octopi, and mammals possess very similar versions of Pax-6. The fact that the same gene helps produce very different types of eyes is most likely due to
A) the few differences in nucleotide sequence among the Pax-6 genes of these organisms.
B) variations in the number of Pax-6 genes among these organisms.
C) the independent evolution of this gene at many different times during animal evolution.
D) differences in the control of Pax-6 expression among these organisms.

Question

Quizplus · Accepted Answer

The fact that Pax-6 produces different types of eyes in different organisms suggests that there are differences in the ways in which it is regulated, or controlled, during development. Other genes and environmental cues may interact with Pax-6 in different ways, resulting in the formation of compound eyes in flies, camera-type eyes in mammals, and other types of eyes in other organisms. Therefore, choice D is the best answer.

All Animals with Eyes or Eyespots That Have Been Studied