In disjunction (separation) of sister chromatids at anaphase

Options

A. centromere moves first and arms trail behind
B. arms move first and centromere trails behind
C. any of the above cases
D. centromere does not move in anaphase

Answer

### Step-by-Step Solution:

1. **Understanding Anaphase**:
- Anaphase is a crucial stage in both mitosis and meiosis where the sister chromatids are separated and pulled towards opposite poles of the cell.

2. **Identifying the Process of Disjunction**:
- Disjunction refers to the separation of sister chromatids during anaphase. This process is essential for ensuring that each daughter cell receives an identical set of chromosomes.

3. **Analyzing the Movement of Chromatids**:
- During anaphase, the centromere, which is the region where the two sister chromatids are joined, plays a key role in the movement.

4. **Determining the Correct Movement**:
- The correct sequence of movement during anaphase is that the centromere moves first, followed by the arms of the chromatids. This means that the centromere leads the way while the arms of the chromatids trail behind.

5. **Conclusion**:
- Based on the analysis, the correct answer to the question about the disjunction of sister chromatids at anaphase is: **Option A: Centromere moves first and arms trail behind.**