The assembly of spindle and disappearance of the nucleolus and nuclear envelope occurs in

Options

A. Metaphase - II
B. Telophase - I
C. Anaphase - II
D. Prophase - II

Answer

To solve the question regarding the assembly of spindle fibers and the disappearance of the nucleolus and nuclear envelope, we need to analyze the stages of meiosis mentioned in the options: metaphase II, telophase I, anaphase II, and prophase II.

### Step-by-Step Solution:

1. **Understanding Meiosis Stages**:
- Meiosis consists of two rounds of division: Meiosis I and Meiosis II, each having several phases (prophase, metaphase, anaphase, telophase).

2. **Analyzing Each Option**:
- **Metaphase II**: During this phase, chromosomes align at the metaphase plate. The spindle fibers are present, but the nucleolus and nuclear envelope are not disappearing at this stage.
- **Telophase I**: In this phase, the nucleolus and nuclear envelope re-form around the separated chromosomes. This is not the phase where they disappear.
- **Anaphase II**: Here, sister chromatids are pulled apart towards opposite poles. The nucleolus and nuclear envelope have already disappeared by this stage.
- **Prophase II**: This is the phase where the chromosomes condense, and the spindle apparatus begins to form. Importantly, this is also when the nucleolus and nuclear envelope disappear.

3. **Conclusion**:
- The assembly of spindle fibers and the disappearance of the nucleolus and nuclear envelope occurs in **Prophase II**.

### Final Answer:
The correct answer is **Prophase II**.