Centrioles arise from

Options

A. (a) pre-existing centrioles
B. (b) de novo
C. (c) nuclear envelope
D. (d) sphaerosome

Explanation

**Step-by-Step Solution:**

1. **Understanding Centrioles**: Centrioles are cylindrical rod-shaped structures made up of microtubular proteins. They are typically found in pairs near the nucleus of eukaryotic animal cells.

2. **Characteristics of Centrioles**: Centrioles do not have a membrane, nor do they contain DNA or RNA. Despite this lack of genetic material, they are capable of replicating themselves.

3. **Mechanism of Replication**: The ability of centrioles to replicate arises from the presence of pericentriolar satellite regions. These regions act as nucleating centers that facilitate the formation of new centrioles.

4. **Source of New Centrioles**: Since centrioles can only form from existing structures, they arise from pre-existing centrioles. This means that during cell division, the centrioles duplicate themselves, and new centrioles are formed from the existing ones.

5. **Function of Centrioles**: The primary function of centrioles is to form spindle fibers, which are crucial for the separation of chromosomes during cell division.

6. **Conclusion**: Therefore, the correct answer to the question "Centrioles arise from" is option A: pre-existing centrioles.

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