The Following Questions Refer to the Description Below

question 53

Multiple Choice

The following questions refer to the description below.
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.
-Pax-6 usually causes the production of a type of light-receptor pigments. In vertebrate eyes, though, a different gene (the rh gene family) is responsible for the light-receptor pigments of the retina. The rh gene, like Pax-6, is ancient. In the marine ragworm, for example, the rh gene causes production of c-opsin, which helps regulate the worm's biological clock. Which of these most likely accounts for vertebrate vision?

• A)The Pax-6 gene mutated to become the rh gene among early mammals.
• B)During vertebrate evolution, the rh gene for biological clock opsin was co-opted as a gene for visual receptor pigments.
• C)In animals more ancient than ragworms, the rh gene(s)coded for visual receptor pigments; in lineages more recent than ragworms, rh has flip-flopped several times between producing biological clock opsins and visual receptor pigments.
• D)Pax-6 was lost from the mammalian genome, and replaced by the rh gene much later.

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Definitions:

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The process by which individuals perceive, think, and gain understanding of their world through the interaction of genetic and learned factors.

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