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

question 21

Multiple Choice

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.

---

Definitions:

Spatial Ability

The ability to mentally rotate objects.

Cognitive Rotation

The mental ability to rotate objects or oneself in three-dimensional space to analyze or solve spatial problems.

Mental Imagery

The representation of sensory experiences in the mind, which can include visual, auditory, and other sensory systems, in the absence of external stimuli.

Obstetricians

Medical doctors specializing in the care of women during pregnancy, childbirth, and the postpartum period.