A DNA molecule in E. coli is heavy and labelled with `N^(15)`. Iit is allowed to replicate in a medium containing `N^(14)`. After one generation of replication, the two daughter molecules will

Options

A. be similar in density but differ from that of parent of DNA
B. differ in density as well as from that of the parent DNA
C. have same density as that of parent DNA
D. differ in density but resemble that parent DNA

Answer

To solve the question regarding the replication of a DNA molecule in E. coli that is heavy and labeled with \( N^{15} \) and then allowed to replicate in a medium containing \( N^{14} \), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Initial Condition**:
- The original DNA molecule is labeled with \( N^{15} \), which means it is heavy due to the presence of the heavier nitrogen isotope.

2. **Semi-Conservative Replication**:
- DNA replication is semi-conservative, meaning that each strand of the original DNA serves as a template for the new strand. Therefore, after replication, each daughter DNA molecule will consist of one original (parent) strand and one newly synthesized strand.

3. **Replication in \( N^{14} \) Medium**:
- The DNA is allowed to replicate in a medium containing \( N^{14} \). This means that the newly synthesized strands will incorporate the lighter nitrogen isotope \( N^{14} \).

4. **Formation of Daughter Molecules**:
- After one generation of replication, we will have two daughter DNA molecules. Each of these molecules will consist of:
- One strand that is heavy (\( N^{15} \)) from the original DNA.
- One strand that is light (\( N^{14} \)) from the replication in the new medium.

5. **Conclusion**:
- Therefore, after one generation of replication, the two daughter molecules will each have one heavy strand and one light strand. This results in two hybrid DNA molecules, each with a density that is intermediate between the heavy and light DNA.

### Final Answer:
After one generation of replication, the two daughter molecules will each consist of one heavy strand (labeled with \( N^{15} \)) and one light strand (labeled with \( N^{14} \)).

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