SAT Subject Biology Practice Question 207: Answer and Explanation

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Question: 207

17. The graph shows the body size distribution in a population. Which statement describes the effects of directional selection on the distribution?

A. The mean shifts, and the curve remains the same.
B. The mean shifts, and the curve becomes narrower.
C. The mean remains the same, and the curve becomes wider.
D. The mean remains the same, and the curve becomes narrower.
E. The mean shifts to both the left and the right, and two new curves form.

Correct Answer: A

Explanation:

Directional selection results in a shift in the mean value for a continuous trait, such as body size, with no change in the variation among individuals. The curve shifts to the left or right without changing shape.

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