Cells of certain species of animals have six pairs of chromosomes. How many molecules of DNA will remain in a nucleus of these animals during `G_(2)` phase?

Options

A. 12
B. 48
C. 8
D. 24

Answer

To solve the problem of how many molecules of DNA will remain in the nucleus of animals with six pairs of chromosomes during the G2 phase, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Number of Chromosomes:**
- The problem states that there are six pairs of chromosomes. Since each pair consists of two chromosomes, the total number of chromosomes can be calculated as:
\[ \text{Total chromosomes} = 6 \text{ pairs} \times 2 = 12 \text{ chromosomes} \]

2. **Understand the DNA Content in G1 Phase:**
- In the G1 phase of the cell cycle, the amount of DNA corresponds to the number of chromosomes. Therefore, if there are 12 chromosomes, there are also 12 molecules of DNA in the G1 phase.

3. **DNA Replication in S Phase:**
- During the S phase (Synthesis phase), DNA replication occurs. This means that each chromosome is duplicated, resulting in double the amount of DNA. Thus, after the S phase:
\[ \text{DNA molecules after S phase} = 12 \text{ (original)} \times 2 = 24 \text{ molecules of DNA} \]

4. **DNA Content in G2 Phase:**
- The G2 phase follows the S phase, and the amount of DNA remains the same as it was at the end of the S phase. Therefore, during the G2 phase, the number of DNA molecules is:
\[ \text{DNA molecules in G2 phase} = 24 \text{ molecules of DNA} \]

5. **Conclusion:**
- The final answer to the question is that there will be **24 molecules of DNA** in the nucleus of these animals during the G2 phase.

### Final Answer:
**24 molecules of DNA**