The Insect Body Plan Includes Many Groups of Serially Repeated

question 56

Multiple Choice

The insect body plan includes many groups of serially repeated units. For example, there are typically three pairs of legs, one on each of the three segments of the thorax. Which of the following options best describes how these pairs of legs develop and evolve?

• A) A single gene controls the development of all six legs. Thus within a species, all three pairs of legs are identical.
• B) The leg pairs all influence each other during development. Gene products move by diffusion from one segment to the other. Therefore, it is impossible to alter the development and form of one pair of legs without causing similar changes in the other two pairs of legs.
• C) The body parts develop in a modular fashion. Therefore, a genetic change could alter the development of one pair of limbs without noticeably changing the rest of the insect's body plan.
• D) The leg pairs grow under the control of an ancient set of highly conserved genes. Therefore, all insects have more or less identical legs. Other parts of the insect body plan can evolve somewhat more freely.

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Definitions:

MR < MC

A scenario where marginal revenue is less than marginal cost, suggesting it is not profitable to produce additional units.

Marginal Cost

A measurement of the cost incurred by producing one additional unit of a product or service.

Average Variable Cost

The per-unit cost that varies, calculated through the division of total variable costs by the quantity of products made.

Economic Profits

The financial gain made in a transaction after accounting for both explicit and implicit costs.