MCAT Biology Question 19: Answer and Explanation
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Question: 19
4. A researcher wishes to incorporate a radiolabeled deoxyadenine into the genome of one of the two daughter cells that would arise as a result of mitosis. What is the latest stage of cellular development during which the radiolabeled deoxyadenine could be added to achieve this result?
- A. G1
- B. G2
- C. M
- D. S
Correct Answer: D
Explanation:
To ensure that the labeled deoxyadenine will be incorporated into the DNA of one of the daughter cells, we have to insert the nucleotide before DNA replication has been completed. Because replication occurs during S stage, we could introduce the deoxyadenine during G1 or S stage. Because G1 precedes S, the latest point the deoxyadenine could be added is the S stage.