Which of the events listed below is not observed during mitosis?

Options

A. chromatic condensation
B. Movement of centrioles to opposite poles
C. Appearance of chromosomes with two chromatids joined together at the centromere
D. Crossing over

Explanation

To answer the question "Which of the events listed below is not observed during mitosis?", we will analyze the events that occur during mitosis and identify the one that does not belong.

### Step-by-Step Solution:

1. **Understanding Mitosis**: Mitosis is a process of cell division that results in two daughter cells, each having the same number of chromosomes as the parent cell. It consists of several phases: prophase, metaphase, anaphase, and telophase.

2. **Identifying Events in Mitosis**:
- **Prophase**: Chromatin condenses into visible chromosomes, the nuclear membrane disappears, and cell organelles may also disappear.
- **Metaphase**: Chromosomes align at the equatorial plane of the cell, and spindle fibers attach to the centromeres of the chromosomes.
- **Anaphase**: Sister chromatids separate and move towards opposite poles of the cell.
- **Telophase**: Nuclear membranes reform around the two sets of chromosomes, and the cell organelles reappear.

3. **Analyzing the Options**:
- **Chromatin Condensation**: This occurs during prophase.
- **Movement of Chromatids to Opposite Poles**: This occurs during anaphase.
- **Appearance of Chromosomes with Two Chromatids**: This occurs during prophase and metaphase.
- **Crossing Over**: This is a process that occurs during meiosis, not mitosis.

4. **Conclusion**: The event that is not observed during mitosis is **crossing over**.

### Final Answer:
The event that is not observed during mitosis is **crossing over**.

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