Pax-6 usually causes the production of a type of light-receptor pigment. 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.

Question

Quizplus · Accepted Answer

The question states that in vertebrates, the rh gene family is responsible for the production of light-receptor pigments in the retina. While Pax-6 is involved in the production of light-receptor pigments, it is not responsible for the pigments in vertebrate eyes. The question also states that the rh gene is ancient and has been shown to cause the production of c-opsin in the marine ragworm, which helps regulate its biological clock. Therefore, it is more likely that during vertebrate evolution, the rh gene for biological clock opsin was co-opted as a gene for visual receptor pigments.

Pax-6 Usually Causes the Production of a Type of Light-Receptor