Which of the two events restore the normal number of chromosomes in life cycle?

Options

A. Mitosis and Meiosis
B. Meiosis and fertilisation
C. Fertilisation and mitosis
D. Only meiosis

Answer

To answer the question "Which of the two events restore the normal number of chromosomes in the life cycle?", we can break down the solution into the following steps:

### Step-by-Step Solution:

1. **Understanding Mitosis**:
- Mitosis is a type of cell division that results in two daughter cells, each having the same number of chromosomes as the parent cell. It is known as an equational division because the chromosome number remains constant.
- **Hint**: Remember that mitosis maintains the chromosome number.

2. **Understanding Meiosis**:
- Meiosis is a reductional division that occurs in the formation of gametes (sperm and eggs). It reduces the chromosome number by half, resulting in haploid cells.
- **Hint**: Meiosis is responsible for halving the chromosome number.

3. **Understanding Fertilization**:
- Fertilization is the process where a male gamete (sperm) and a female gamete (egg) fuse to form a zygote. This zygote restores the diploid chromosome number because it combines the haploid sets from each parent.
- **Hint**: Fertilization combines gametes to restore the diploid state.

4. **Connecting the Concepts**:
- To maintain the normal number of chromosomes in a life cycle, we need to consider the processes that balance the reduction caused by meiosis. Meiosis produces haploid gametes, and fertilization brings these gametes together to form a diploid zygote.
- **Hint**: Think about how meiosis and fertilization work together in the life cycle.

5. **Conclusion**:
- The two events that restore the normal number of chromosomes in the life cycle are **meiosis and fertilization**. Meiosis creates haploid gametes, and fertilization combines these gametes to form a diploid zygote, thus maintaining the chromosome number throughout generations.
- **Final Answer**: The correct option is **meiosis and fertilization**.