Major check point of cell cycle is

Options

A. `G_(1)to S` transition
B. `S to G_(1)` transition
C. `G_(2) to M` transition
D. `Mto G_(2)` transition

Answer

### Step-by-Step Text 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 is crucial for the proper division and function of cells.

2. **Role of Checkpoints**: Checkpoints are critical control mechanisms in the cell cycle that ensure the cell is ready to proceed to the next phase. They assess whether the cell's DNA is intact and whether the cell has the necessary resources to divide.

3. **Identifying Major Checkpoints**: There are several checkpoints in the cell cycle, but the major ones are:
- **G1 Checkpoint**: Checks for cell size, nutrients, and DNA integrity before entering the S phase.
- **G2 Checkpoint**: Ensures that DNA replication has occurred correctly and checks for DNA damage before entering mitosis.
- **M Checkpoint (Spindle Checkpoint)**: Ensures that all chromosomes are properly attached to the spindle apparatus before proceeding with mitosis.

4. **Focusing on the G1/S Transition Checkpoint**: Among these checkpoints, the G1/S transition checkpoint is particularly critical. It checks whether the cell is ready to enter the S phase, where DNA replication occurs. If there are any issues (like DNA damage), the cell can halt progression and either repair the damage or undergo apoptosis (programmed cell death).

5. **Conclusion**: The major checkpoint of the cell cycle is the **G1/S Transition Checkpoint**. This checkpoint is vital for ensuring that cells do not replicate damaged DNA, which could lead to mutations and cancer.