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Practice MCAT Question - Q75 - Answer!

Chromosomes are visible during mitosis and meiosis when they condense and are tightly coiled. Yet, they cannot be seen as distinct units at other times in the cell cycle when their chromatin material is uncoiled. What reason best explains this phenomenon?

A.  They must uncoil to reveal genetic sequences during protein synthesis.
B.  They must uncoil to reveal all DNA sequences during replication.
C.  They must be tightly coiled for them to be moved around during cell reproduction.
D.  All of the above

The correct answer is (D). Clearly, precise DNA sequences must be revealed during transcription of genes, as well as during the complete replication of each DNA strand. In this “uncoiled” condition, the chromosomes cannot be seen as distinct units. In contrast, to move chromosomes around within the cell during prophase, metaphase, anaphase, and telophase would be virtually impossible if they remained uncoiled.

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