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 analyze the mechanisms involved in preventing this phenomenon and identify which option does not contribute to this prevention.

### Step-by-Step Solution:

1. **Understanding Polyspermy**:
- Polyspermy occurs when an egg is fertilized by more than one sperm. This results in a non-functional zygote that cannot develop into a proper embryo.

2. **Mechanisms to Prevent Polyspermy**:
- The female body has developed several mechanisms to prevent polyspermy:
- **Fast Block**: This mechanism involves electrical changes in the egg membrane. When a sperm enters the egg, sodium channels open, leading to depolarization of the membrane. This change in charge prevents other sperm from entering.
- **Cortical Reaction**: After the first sperm enters, the egg releases cortical granules that modify the zona pellucida, making it impenetrable to additional sperm.
- **Zonal Reaction**: The zona pellucida hardens after the first sperm fertilizes the egg, further preventing additional sperm from entering.

3. **Analyzing the Options**:
- **Option A**: Electrical changes in the egg membrane (depolarization) - This is correct as it prevents polyspermy.
- **Option B**: Cortical reaction - This is also correct as it prevents polyspermy.
- **Option C**: Zona reactions - This is correct as it prevents polyspermy.
- **Option D**: Sodium gates in the egg membrane getting closed - This is incorrect because the sodium gates need to be open for depolarization to occur, which prevents polyspermy.

4. **Conclusion**:
- The option that does not contribute to the prevention of polyspermy is **Option D: Sodium gates in the egg membrane getting closed**.

### Final Answer:
**Option D** is the correct answer as it does not prevent polyspermy.

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