SAT Subject Biology Practice Question 29: Answer and Explanation

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Question: 29

3. At which stage in meiosis are sister chromatids of each chromosome identical?

I. Beginning of prophase I

II. Beginning of metaphase I

III. End of telophase I

A. I only
B. II only
C. III only
D. I and II
E. II and III

Correct Answer: A

Explanation:

Chromosomes start out as identical sister chromatids. These exchange DNA with nonidentical homologous chromatids during crossing over, resulting in homologs made up of nonidentical sister chromatids. Crossing over happens in prophase I; therefore, all subsequent stages feature nonidentical sister chromatids.

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