Which of the following not occurs in Anaphase-I but occurs in Anaphase-II:-

Options

A. Condensation of chromosomes
B. Poleward movement of chromosome
C. Contraction of spindle fibers
D. Splitting of centromere

Answer

To solve the question "Which of the following does not occur in Anaphase-I but occurs in Anaphase-II?", we will analyze each of the given options step by step.

### Step 1: Understand the Events of Anaphase-I and Anaphase-II
- **Anaphase-I**: This phase is characterized by the separation of homologous chromosomes. The chromosomes move towards opposite poles, but the centromeres do not split.
- **Anaphase-II**: This phase is similar to mitosis, where the sister chromatids are separated. The centromeres split, allowing the sister chromatids to move towards opposite poles.

### Step 2: Analyze Each Option
1. **Condensation of Chromosomes**:
- This occurs during prophase, not during anaphase. Therefore, it is not relevant to the question.

2. **Poleward Movement of Chromosomes**:
- This occurs in both Anaphase-I and Anaphase-II. In Anaphase-I, homologous chromosomes move towards the poles. Thus, this option does not answer the question.

3. **Shortening of the Spindle Fibers**:
- This occurs during both Anaphase-I and Anaphase-II as the spindle fibers contract to pull the chromosomes apart. Hence, this option is also not the correct answer.

4. **Splitting of Centromere**:
- This is a key event that occurs in Anaphase-II. In Anaphase-I, the centromeres do not split; they only split in Anaphase-II, allowing the sister chromatids to separate.

### Step 3: Conclusion
Based on the analysis, the event that does not occur in Anaphase-I but occurs in Anaphase-II is the **splitting of centromeres**. Therefore, the correct answer is **Option 4**.

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