The critical checkpoints that control the cell cycle are at the:

Options

A. `G_1` to s stage and `G_2` to M stage
B. S to `G_2` stage and G2 to M stage
C. M to `G_1` stage and `G_2` to M stage
D. M to `G_1` stage and S to `G_2` stage

Answer

To answer the question about the critical checkpoints that control the cell cycle, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Cell Cycle**:
- The cell cycle consists of several phases: G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis). Each phase has specific functions and is crucial for proper cell division.

2. **Identifying Checkpoints**:
- Checkpoints are regulatory mechanisms that ensure the proper progression of the cell cycle. They assess whether the cell is ready to proceed to the next phase.

3. **Key Checkpoints**:
- The main checkpoints in the cell cycle are:
- **G1 to S Checkpoint**: This checkpoint checks for cell size, nutrients, growth factors, and DNA integrity before the cell commits to DNA replication.
- **G2 to M Checkpoint**: This checkpoint ensures that DNA has been completely and accurately replicated before the cell enters mitosis.

4. **Evaluating the Options**:
- Now, we can evaluate the provided options based on our understanding of the checkpoints:
- **Option A**: G1 to S stage and G2 to M stage (Correct)
- **Option B**: S to G2 stage and G2 to M stage (Incorrect)
- **Option C**: M to G1 stage and G2 to M stage (Incorrect)
- **Option D**: M to G1 stage and S to G2 stage (Incorrect)

5. **Conclusion**:
- The critical checkpoints that control the cell cycle are at the G1 to S stage and G2 to M stage. Therefore, the correct answer is **Option A**.