DNA with only 15N is grown for two generations in 14N medium. What is the content of the DNA molecules after the second replication?
Answer and explanation
Correct answer: C. Half are hybrid (15N and 14N) and half contain 14N only
- Step 1: Replication is semi-conservative: each new molecule keeps one old strand. Step 2. After one round all are hybrid. After the second, 2 of 4 are hybrid and 2 of 4 are light. Answer: Half hybrid, half 14N only. Why not the others: 'All hybrid' describes only the first generation.
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