In prophase of mitosis, which one of the following events occurs in animal cells but not in plant cells?

Options

A. Centrioles migrate to opposite sides of the nucleus
B. Homologous chromosomes do not associate
C. The nuclear envelope (membrane) breaks down
D. Nucleoli disappear

Answer

**Step-by-Step Solution:**

1. **Understanding Prophase in Mitosis:**
- Prophase is the first stage of mitosis, where several key events occur to prepare the cell for division.

2. **Identifying Key Features of Prophase:**
- During prophase, chromatin condenses into visible chromosomes, the nuclear envelope begins to break down, and the mitotic spindle starts to form.

3. **Role of Centrioles:**
- In animal cells, centrioles play a crucial role in the formation of the spindle apparatus. They duplicate during the S phase and move to opposite poles of the cell.

4. **Centriole Presence in Animal vs. Plant Cells:**
- Centrioles are present in animal cells but are absent in plant cells. This is a significant difference between the two types of cells.

5. **Conclusion:**
- Since the centriole is responsible for organizing the spindle fibers and is only present in animal cells, the event that occurs in prophase of mitosis in animal cells but not in plant cells is the migration of centrioles to opposite poles.

**Final Answer:**
The event that occurs in prophase of mitosis in animal cells but not in plant cells is the migration of centrioles to opposite poles.

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