In which phase of the cell cycle, the amount of DNA in a cell remains constant at 4C level, considering that the initial amount of DNA was 2C ?

Options

A. `G_0 and G_1`
B. `G_1 and S`
C. Only `G_2`
D. `G_2` and M

Answer

To determine in which phase of the cell cycle the amount of DNA in a cell remains constant at the 4C level, given that the initial amount of DNA was 2C, we can analyze the different phases of the cell cycle step by step.

### Step-by-Step Solution:

1. **Understanding the Cell Cycle**:
- The cell cycle consists of two main phases: Interphase and M phase (mitosis).
- Interphase is further divided into three sub-phases: G1, S, and G2.

2. **Initial DNA Content**:
- The initial amount of DNA is given as 2C. This represents the diploid state of the cell before DNA replication.

3. **G1 Phase**:
- In the G1 phase, the cell is metabolically active, grows, and synthesizes proteins.
- The amount of DNA remains at 2C during this phase.

4. **S Phase (Synthesis Phase)**:
- During the S phase, DNA replication occurs.
- The amount of DNA doubles from 2C to 4C as each chromosome is replicated.

5. **G2 Phase**:
- In the G2 phase, the cell continues to grow and prepares for mitosis.
- The amount of DNA remains constant at 4C because no further replication occurs after the S phase.

6. **M Phase (Mitosis)**:
- During the M phase, the cell divides. However, the amount of DNA is not constant during this phase as it is distributed into daughter cells.

7. **Conclusion**:
- The amount of DNA remains constant at 4C during the G2 phase of the cell cycle.

### Final Answer:
The correct answer is **c. Only G2**.