SAT Subject Biology Practice Question 164: Answer and Explanation

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Question: 164

14. During mitosis, a checkpoint ensures that all chromosomal kinetochore proteins, present at the centromere of each sister chromatid, are attached to spindle fibers. Kinetochore proteins that are unattached produce a signal that prevents mitosis from proceeding to the next stage. This checkpoint occurs at the transition from

A. anaphase to telophase
B. prophase to metaphase
C. metaphase to telophase
D. prophase to anaphase
E. metaphase to anaphase

Correct Answer: E

Explanation:

Sister chromatids line up at the metaphase plate, and spindle fibers attach to kinetochore proteins at the centromeres. All sister chromatids must be present and attached to spindle fibers in order to prevent nondisjunction during anaphase. An unattached kinetochore protein generates a signal that prevents the transition from metaphase to anaphase.

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