All Animals with Eyes or Eyespots That Have Been Studied

question 18

Multiple Choice

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.

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