If 50 heavy DNA `(N^(15))` molecules are replicated 2 times in `N^(14)` medium, what is obtained?

Options

A. genotype
B. gene pool
C. gene factor
D. none of the above

Answer

To solve the problem of what is obtained when 50 heavy DNA (N^15) molecules are replicated two times in N^14 medium, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Initial Condition**:
- We start with 50 heavy DNA molecules, which are labeled with N^15. This means that all the nitrogen bases in these DNA molecules contain the heavier isotope of nitrogen (N^15).

2. **First Replication in N^14 Medium**:
- When these DNA molecules are replicated for the first time in a medium containing N^14, each original heavy DNA strand (N^15) will serve as a template for the synthesis of a new complementary strand.
- The result of this replication will be:
- Each of the 50 original N^15 strands will pair with a newly synthesized N^14 strand.
- Thus, after the first replication, we will have 50 DNA molecules that are hybrids: each will consist of one N^15 strand and one N^14 strand.

3. **Counting the Molecules After First Replication**:
- After the first replication, we have 50 hybrid DNA molecules, each containing one N^15 and one N^14 strand.

4. **Second Replication in N^14 Medium**:
- Now, these 50 hybrid DNA molecules (N^15/N^14) will undergo a second round of replication in the N^14 medium.
- During this replication:
- Each N^15 strand will again serve as a template, producing a new N^14 strand.
- Each N^14 strand from the first replication will also serve as a template, producing another N^14 strand.

5. **Counting the Molecules After Second Replication**:
- After the second replication, we will have:
- 50 strands that are N^15/N^14 (from the first replication) will yield 50 new strands that are N^14.
- Additionally, the 50 strands that were N^14 from the first replication will also yield 50 new strands that are N^14.
- Therefore, the final count of DNA molecules will be:
- 50 hybrid (N^15/N^14) and 100 N^14 strands.

6. **Final Composition**:
- In total, after two rounds of replication, we will have:
- 50 DNA molecules with one N^15 and one N^14 strand (hybrid).
- 100 DNA molecules with both strands as N^14.

### Conclusion:
The final result of replicating 50 heavy DNA (N^15) molecules two times in N^14 medium will yield a mixture of DNA molecules:
- 50 hybrid molecules (N^15/N^14)
- 100 molecules with both strands as N^14.