Which event does not occur during prophase in an animal cell?

Options

A. Nuclear envelope disperses
B. Chromosomes replicate
C. Spindle begins to form
D. Chromosomes condense

Answer

To determine which event does not occur during prophase in an animal cell, let's analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Prophase**: Prophase is the first stage of mitosis, where several key events occur as the cell prepares to divide.

2. **Analyzing Option A: Nuclear Envelope Disperses**:
- During prophase, the nuclear envelope begins to break down or disperse. This is a key event that allows the chromosomes to move freely within the cell.
- **Conclusion**: This event occurs during prophase.

3. **Analyzing Option B: Chromosomes Replicate**:
- Chromosome replication occurs during the S phase (Synthesis phase) of the cell cycle, which takes place before mitosis begins.
- By the time prophase starts, the chromosomes have already been replicated and are in their condensed form.
- **Conclusion**: This event does NOT occur during prophase.

4. **Analyzing Option C: Spindle Begins to Form**:
- During prophase, the spindle apparatus starts to form, which is essential for the separation of chromosomes later in mitosis.
- **Conclusion**: This event occurs during prophase.

5. **Analyzing Option D: Chromosomes Condense**:
- One of the hallmark events of prophase is the condensation of chromosomes, making them visible under a microscope.
- **Conclusion**: This event occurs during prophase.

### Final Answer:
The event that does not occur during prophase in an animal cell is **B. Chromosomes replicate**.

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