The Genes That Specify Where and When Photoreceptors Arise During

question 24

Multiple Choice

The genes that specify where and when photoreceptors arise during embryonic development are shared among flatworms, annelids, arthropods, and vertebrates. What can we conclude from this observation?

• A) Members of these four groups are more closely related to each other than to other groups.
• B) What humans see is very similar to the images seen by flatworms, annelids, and arthropods.
• C) The genetic underpinnings of all photoreceptors were present in the earliest bilaterian animals.
• D) A single-lens eye has been favored throughout most of animal evolution.

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Definitions:

Turgor

The state of being swollen or distended, typically used to describe the elasticity of the skin as an indicator of hydration and health.

Dehydration

A condition resulting from excessive loss of body water, leading to imbalances in essential minerals and electrolytes.

Ptosis

The drooping or falling of the upper eyelid, which can be due to various causes including nerve damage, muscle diseases, or congenital conditions.

Ectropion

A condition where the eyelid turns outward, exposing the inner eyelid and eyeball, which can lead to irritation and discomfort.