To solve the question regarding the interphase events (G1, S, G2) that occur before the commencement of mitosis, meiosis-I, meiosis-II, and binary fission of bacteria, we can analyze each option step by step.
### Step-by-Step Solution:
1. **Understanding Interphase**:
- Interphase is the phase of the cell cycle where the cell prepares for division. It consists of three stages: G1 (Gap 1), S (Synthesis), and G2 (Gap 2).
- During G1, the cell grows and synthesizes proteins necessary for DNA replication.
- The S phase is where DNA replication occurs, resulting in two copies of each chromosome.
- In G2, the cell continues to grow and prepares for mitosis by synthesizing proteins and organelles.
2. **Analyzing Mitosis**:
- Mitosis is the process of cell division that follows interphase. Therefore, the events of G1, S, and G2 must occur before mitosis can begin.
- **Conclusion**: Interphase occurs before mitosis.
3. **Analyzing Meiosis-I**:
- Meiosis-I is the first division in meiosis and also requires the cell to go through interphase (G1, S, G2) to prepare for the division.
- **Conclusion**: Interphase occurs before meiosis-I.
4. **Analyzing Meiosis-II**:
- Meiosis-II follows meiosis-I and does not require a complete interphase. After meiosis-I, there is a short phase called interkinesis, but no DNA replication occurs during this phase.
- **Conclusion**: Interphase does not occur before meiosis-II.
5. **Analyzing Binary Fission of Bacteria**:
- Binary fission is a form of asexual reproduction in bacteria. Bacteria do not have a defined interphase like eukaryotic cells; they replicate their DNA and divide without the stages of G1, S, and G2.
- **Conclusion**: Interphase does not occur before binary fission.
### Final Answer:
The definite events of G1, S, and G2 stages occur before the commencement of:
- I. Mitosis (Yes)
- II. Meiosis-I (Yes)
- III. Meiosis-II (No)
- IV. Binary fission of bacteria (No)
Thus, the correct options are **I and II**.
