During fertilization, cortical and zona reactions are caused due to

Options

A. `Ca^(++)` wave in sperm
B. Enzymes of acrosome
C. `Ca^(++)` wave in oocyte
D. Capacitation

Answer

### Step-by-Step Solution:

1. **Understanding Fertilization**:
- Fertilization is the process where a sperm cell merges with an oocyte (egg) to form a zygote. This process triggers several reactions in the oocyte.

2. **Identifying Cortical and Zona Reactions**:
- The **cortical reaction** involves the release of cortical granules from the oocyte after fertilization. This helps prevent polyspermy (the entry of multiple sperm into the egg).
- The **zona reaction** refers to changes in the zona pellucida (the protective layer surrounding the oocyte) that also prevent polyspermy.

3. **Role of Calcium Ions**:
- Calcium ions (Ca²⁺) play a crucial role in initiating both the cortical and zona reactions. The influx of calcium ions into the oocyte triggers these reactions.

4. **Source of Calcium Ions**:
- The calcium wave that leads to these reactions originates from the oocyte, not from the sperm. This is essential for the proper response of the oocyte to fertilization.

5. **Evaluating the Options**:
- **Calcium wave in sperm**: Incorrect, as the calcium wave responsible for the reactions comes from the oocyte.
- **Enzyme of acrosome**: Incorrect, as the acrosome's enzymes help in penetrating the zona pellucida but do not trigger the cortical and zona reactions.
- **Calcium wave in oocytes**: Correct, as the calcium wave in the oocyte is responsible for initiating the cortical and zona reactions.
- **Capacitation**: Incorrect, as this refers to the process that sperm undergo to gain the ability to fertilize an egg, not the reactions following fertilization.

6. **Conclusion**:
- The correct answer is that the cortical and zona reactions during fertilization are caused by the **calcium wave in oocytes**.

### Final Answer:
The cortical and zona reactions during fertilization are caused by the **calcium wave in oocytes**.

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