Chromosome number is restored by

Options

A. Meiosis
B. Mitosis
C. Crossing over
D. Interphase

Answer

### Step-by-Step Solution:

1. **Understanding Chromosome Number Restoration**:
- The term "restoration of chromosome number" refers to the process where the chromosome count returns to its original state after it has been halved. This typically occurs during the life cycle of an organism.

2. **Identifying the Process**:
- The key process that leads to the restoration of chromosome number is fertilization. In sexual reproduction, gametes (sperm and egg) are produced through meiosis, which reduces the chromosome number by half.

3. **Meiosis Explained**:
- Meiosis is a type of cell division that results in four daughter cells, each with half the number of chromosomes of the parent cell. This is known as reductional division, where diploid cells (2n) divide to form haploid cells (n).

4. **Formation of Gametes**:
- During meiosis, male and female gametes are formed. For example, a diploid organism will produce haploid gametes through meiosis, which then combine during fertilization.

5. **Fertilization**:
- When a sperm fertilizes an egg, the haploid gametes combine to form a diploid zygote. This zygote has the same chromosome number as the original diploid parent, thus restoring the chromosome number.

6. **Conclusion**:
- Therefore, the process that restores the chromosome number is meiosis, followed by fertilization.

### Final Answer:
**Chromosome number is restored by meiosis.**

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