Two nuclear divisions occur during meiosis: meiosis I and meiosis II. Meiosis reduces chromosome number and introduces genetic variations in offsprings.Which of the following events does not occur during prophase I in meiosis?

Options

A. Crossing-over between homologous chromosomes
B. Pairing of homologous chromosomes
C. Disintegration of spindle fibres
D. Formation of spindle fibres

Answer

To determine which event does not occur during prophase I of meiosis, we need to analyze the key events that take place during this stage.

### Step-by-Step Solution:

1. **Understanding Prophase I**: Prophase I is the first stage of meiosis I. It is characterized by several critical events that prepare the cell for division.

2. **Chromosome Condensation**: During prophase I, chromosomes condense and become visible under a microscope. Each chromosome consists of two sister chromatids.

3. **Synapsis and Crossing Over**: Homologous chromosomes pair up in a process called synapsis, forming tetrads. This is also the stage where crossing over occurs, allowing for genetic recombination.

4. **Nuclear Membrane**: The nuclear membrane remains intact during prophase I. It does not disintegrate until later in the process, specifically at the end of prophase I.

5. **Formation of Spindle Fibers**: Spindle fibers begin to form from the centrioles during prophase I. These fibers are essential for the movement of chromosomes during cell division.

6. **Disintegration of Spindle Fibers**: The disintegration of spindle fibers does not occur during prophase I. Instead, spindle fibers are forming and preparing for the separation of chromosomes in later stages.

7. **Conclusion**: Based on the analysis, the event that does not occur during prophase I is the disintegration of spindle fibers.

### Final Answer:
The event that does not occur during prophase I in meiosis is the **disintegration of spindle fibers**.

---