Polysemy is prevented by all the events , except

Options

A. Electrical changes in the egg membrane, depolarisation
B. Cortical reaction
C. Zona reaction
D. Sodium gates in the egg membrane getting close

Answer

To solve the question regarding the prevention of polyspermy, we need to follow a systematic approach:

### Step-by-Step Solution:

1. **Understanding Polyspermy**:
- Polyspermy refers to the condition where an ovum is fertilized by more than one sperm. This can lead to abnormal development of the embryo.

2. **Methods of Preventing Polyspermy**:
- There are two primary methods to prevent polyspermy:
- **Quick Method**: This involves a rapid increase in the concentration of cytoplasmic calcium in the egg. This calcium influx causes immediate changes that prevent additional sperm from fusing with the egg.
- **Slow Method**: This involves the formation of a fertilization membrane through a process known as the cortical reaction, which occurs after the first sperm has fertilized the egg.

3. **Identifying the Options**:
- We need to evaluate the options provided in the question to see which one does not contribute to the prevention of polyspermy.
- **Option A**: Electrical changes in the egg membrane and depolarization - This is a known method to prevent polyspermy.
- **Option B**: Cortical reaction - This is part of the slow method and helps in preventing polyspermy.
- **Option C**: Zona reaction - This is also a mechanism that prevents polyspermy.
- **Option D**: Sodium gates in the egg membrane getting closed - This is not a recognized method for preventing polyspermy.

4. **Conclusion**:
- Since options A, B, and C are all methods that help prevent polyspermy, while option D does not contribute to this prevention, the correct answer to the question is **Option D**.

### Final Answer:
**Option D** (sodium gates in egg membrane getting closed) does not prevent polyspermy.