The initial step during fertilization of egg is:

Options

A. Penetration of sperm into ovum
B. Fertilizin-antifertilizin reaction
C. Formation of fertilization cone
D. Formation of fertilization membrane

Answer

**Step-by-Step Solution:**

1. **Understanding Fertilization**: Fertilization is the process where a sperm cell unites with an egg cell (ovum) to form a zygote. This process involves several steps, and identifying the initial step is crucial.

2. **Identifying the Options**: The options provided include:
- Penetration of sperm into ovum
- Fertilizing-Anti-Fertilizing Reaction
- Formation of fertilization cone
- Formation of fertilization membrane

3. **Analyzing Each Option**:
- **Penetration of sperm into ovum**: This step occurs after the fertilization reaction has taken place. It is not the initial step.
- **Fertilizing-Anti-Fertilizing Reaction**: This is the interaction between the fertilizing receptors on the ovum and the antifertilizing components on the sperm. This reaction is crucial as it determines which sperm can penetrate the ovum.
- **Formation of fertilization cone**: This occurs after the sperm has penetrated the ovum and is not the first step.
- **Formation of fertilization membrane**: This step occurs to prevent polyspermy after the fertilization reaction has taken place.

4. **Conclusion**: The initial step during fertilization of the egg is the **Fertilizing-Anti-Fertilizing Reaction**. This reaction allows one sperm to bind to the ovum, leading to the subsequent steps of fertilization.

5. **Final Answer**: The correct answer is the **Fertilizing-Anti-Fertilizing Reaction**.

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