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, we need to analyze the different phases of the cell cycle.

### Step-by-Step Solution:

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

2. **Identifying DNA Content**:
- **G1 Phase**: In this phase, the cell grows and prepares for DNA synthesis. The DNA content remains at 2C (the initial amount) because no DNA replication occurs during this phase.
- **S Phase**: This is the phase where DNA replication occurs. Each chromosome is duplicated, resulting in the DNA content increasing to 4C by the end of this phase.
- **G2 Phase**: After DNA replication is complete, the cell enters the G2 phase. The DNA content remains at 4C during this phase as the cell prepares for mitosis. No further DNA replication occurs in G2.

3. **M Phase**: This phase involves the actual division of the cell (mitosis and cytokinesis). The DNA content does not remain constant at 4C during this phase because the cell divides into two daughter cells, each returning to a 2C state.

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

### Final Answer:
The amount of DNA in a cell remains constant at the 4C level during the **G2 phase** of the cell cycle.

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