Meiosis and mitosis differ from each other because in meiosis

Options

A. chromosomes first pair and then reduced to half
B. homologous chromosomes pair and exchange parts
C. 4 nuclei are formed which are not identical
D. all of the above three are correct

Answer

### Step-by-Step Solution:

1. **Understanding Mitosis and Meiosis**:
- Mitosis is a type of cell division that occurs in somatic (body) cells, resulting in two identical daughter cells. It is an equational division, meaning the chromosome number remains the same.
- Meiosis, on the other hand, occurs in reproductive cells (gametes) and results in four non-identical daughter cells. It is a reductional division, meaning the chromosome number is halved.

2. **Analyzing the Options**:
- **Option 1**: "Chromosomes first pair and then reduce it to half."
- This describes the process in meiosis where homologous chromosomes pair up during prophase I and then separate, reducing the chromosome number by half.
- **Option 2**: "Homologous chromosomes pair and exchange their parts."
- This refers to crossing over, which occurs during prophase I of meiosis, where segments of DNA are exchanged between homologous chromosomes, leading to genetic variation.
- **Option 3**: "4 nuclei are found which are not identical."
- In meiosis, after two rounds of division, four non-identical nuclei (daughter cells) are produced, each with half the chromosome number of the original cell.

3. **Conclusion**:
- All three options correctly describe aspects of meiosis. Therefore, the correct answer is **Option 4: All of the above three are correct**.