Which one of the following combinations of chromosome number (n) and DNA content (c) is true of the diplotene stage of mammalian oocyte?

Options

A. 1 n and 2c
B. 2 n and 4c
C. 2 n and 2c
D. 1 n and 4c

Answer

To determine the correct combination of chromosome number (n) and DNA content (c) during the diplotene stage of mammalian oocytes, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Diplotene Stage**:
- The diplotene stage is part of prophase I of meiosis, where homologous chromosomes are paired and begin to separate. This stage is characterized by the presence of bivalents (paired homologous chromosomes).

2. **Identify Chromosome Number (n)**:
- In mammals, oocytes are typically diploid (2n) before meiosis begins. During the diplotene stage, the number of chromosomes remains 2n, as the homologous chromosomes have not yet separated completely.

3. **Determine DNA Content (c)**:
- Each chromosome consists of two sister chromatids at this stage, which means that the DNA content is doubled. Therefore, if the chromosome number is 2n, the DNA content will be 4c (since each chromosome contributes 2c due to the two chromatids).

4. **Analyze the Options**:
- Option A: 1n, 2c (Incorrect)
- Option B: 2n, 4c (Correct)
- Option C: 2n, 2c (Incorrect)
- Option D: 1n, 4c (Incorrect)

5. **Conclusion**:
- The correct combination of chromosome number and DNA content during the diplotene stage of mammalian oocytes is **Option B: 2n and 4c**.