Question

Assuming that 50 heavy (i.e. containing $N^{15}$ ) DNA molecules replicated twice in amedium containing $N^{14}$ , we expect:

• A. 100 half heavy, half-light and 100 light DNA molecules
• B. 100 heavy and 100 light DNA molecules
• C. 50 heavy and 150 light DNA molecules
• D. 50 heavy and 100 light DNA molecules

Answer 1

Answer: (A)

In semi conservative mode of DNA replication new DNA molecule possess one parental strand i.e. heavy $N^{15}$ and one new strand i.e. (Light $N^{14}$ ). Hence, 50heavy DNA molecule in first replication will produce 100 hybrid DNA molecule and is second replication 100 DMA will be hybrid (half heavy and half-light) and 100 light DNA molecules.