In 'S' phase of the cell cycle

Options

A. Amount of DNA remains same in each cell
B. Chromosome number is increased
C. Amount of DNA is reduced to half in each cell
D. Amount of DNA double in each cell.

Answer

**Step-by-Step Solution:**

1. **Understanding the Cell Cycle**: The cell cycle consists of two main phases: interphase and mitotic phase (M phase). Interphase is further divided into three phases: G1 (Gap 1), S (Synthesis), and G2 (Gap 2).

2. **Focusing on the S Phase**: The S phase, also known as the synthesis phase, is crucial because this is when DNA replication occurs.

3. **DNA Replication**: During the S phase, each chromosome is replicated. This means that the amount of DNA in the cell doubles. For example, if a cell starts with 2N DNA content, after the S phase, it will have 4N DNA content.

4. **Consequences of DNA Replication**: As a result of this replication, the total amount of DNA in the cell increases, but the number of chromosomes remains the same. Each chromosome now consists of two sister chromatids.

5. **Finalizing the Correct Option**: Given the options provided:
- Option 1 states that the amount of DNA remains the same, which is incorrect.
- Option 2 states that the chromosome number is increased, which is also incorrect.
- Option 3 states that the amount of DNA is reduced to half, which is incorrect.
- Option 4 states that the amount of DNA doubles in each cell, which is correct.

6. **Conclusion**: Therefore, the correct answer is that the amount of DNA doubles in each cell during the S phase of the cell cycle.