Which centriole of sperm is required for first cleavage?

Options

A. Proximal centriole
B. Distal centriole
C. Ring centriole
D. Posterior centriole

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which centriole of the sperm is necessary for the first cleavage of the fertilized egg.

2. **Identifying the Centrioles**: Sperm cells contain different types of centrioles: proximal centriole, distal centriole, ring centriole, and posterior centriole.

3. **Role of Centrioles in Fertilization**: During fertilization, the sperm contributes its centrioles to the egg. The centrioles play a crucial role in the early stages of cell division.

4. **Focus on the Proximal Centriole**: Among the centrioles present in the sperm, the proximal centriole is specifically responsible for initiating the first cleavage.

5. **Function of the Proximal Centriole**: The proximal centriole helps in the formation of aster rays in the fertilized egg. These aster rays are essential for the proper positioning of the pronuclei (the nuclei of the sperm and egg) during the early stages of cell division.

6. **Conclusion**: Therefore, the centriole of the sperm that is required for the first cleavage is the **proximal centriole**.

**Final Answer**: The proximal centriole (Option A) is required for the first cleavage.

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