Which one occurs once in life cycle ?

Options

A. Replication of DNA
B. Replication of chromosomes
C. Meiosis
D. Mitosis

Answer

To determine which process occurs only once in the life cycle, we can analyze the options provided:

1. **Replication of DNA**: This process occurs every time a cell divides. Cells replicate their DNA to ensure that each daughter cell receives an identical copy of the genetic material. Therefore, this does not occur just once in the life cycle.

2. **Replication of Chromosomes**: Similar to DNA replication, chromosome replication occurs during the cell cycle, specifically during the S phase of interphase, before a cell divides. This also happens multiple times throughout an organism's life cycle, so it is not a one-time event.

3. **Meiosis**: This is a type of cell division that reduces the chromosome number by half, resulting in the formation of gametes (sperm and eggs in animals). Meiosis occurs only once during the life cycle of an organism, specifically during the formation of gametes for sexual reproduction.

4. **Mitosis**: This process is responsible for growth and repair in multicellular organisms. Mitosis occurs repeatedly throughout the life of an organism as cells divide to replace dead or damaged cells, so it is not a one-time event.

Based on this analysis, the correct answer is:

**Meiosis occurs once in the life cycle.**

### Step-by-Step Solution:
1. **Identify the processes listed**: Replication of DNA, Replication of Chromosomes, Meiosis, and Mitosis.
2. **Evaluate each process**:
- **Replication of DNA**: Occurs every cell division.
- **Replication of Chromosomes**: Occurs every cell division.
- **Meiosis**: Occurs once during gamete formation.
- **Mitosis**: Occurs repeatedly for growth and repair.
3. **Conclude**: Only meiosis occurs once in the life cycle.