The number of chromatids in a chromosome at anaphase is

Options

A. One in mitosis, one in meiosis-I and two in meiosis-II
B. One in mitosis, two in meiosis-I and one in meiosis-II
C. Two in mitosis, two in meiosis-I and two in meiosis-II
D. Two in mitosis, two in meiosis-I and two in meiosis-II

Answer

To determine the number of chromatids in a chromosome at anaphase, we need to analyze the process of cell division during both mitosis and meiosis.

### Step-by-Step Solution:

1. **Understanding Chromatids**:
- A chromatid is one half of a duplicated chromosome. After DNA replication, each chromosome consists of two sister chromatids joined at a region called the centromere.

2. **Phases of Mitosis**:
- Mitosis consists of several phases: prophase, metaphase, anaphase, and telophase.
- During metaphase, chromosomes align at the equatorial plane of the cell, and each chromosome consists of two chromatids.

3. **Anaphase in Mitosis**:
- At anaphase, the sister chromatids are pulled apart towards opposite poles of the cell.
- Once the chromatids are separated, each chromatid is considered an individual chromosome.
- Therefore, at anaphase, each chromosome has **1 chromatid**.

4. **Phases of Meiosis**:
- Meiosis consists of two rounds of division: meiosis I and meiosis II.
- In meiosis I, homologous chromosomes are separated, and each chromosome still consists of two chromatids.

5. **Anaphase in Meiosis I**:
- During anaphase I, homologous chromosomes are pulled apart, but each chromosome still consists of two chromatids.
- Thus, at anaphase I, each chromosome has **2 chromatids**.

6. **Anaphase in Meiosis II**:
- In meiosis II, the sister chromatids are separated just like in mitosis.
- Therefore, at anaphase II, each chromosome has **1 chromatid**.

7. **Conclusion**:
- In summary:
- At anaphase of mitosis: 1 chromatid per chromosome.
- At anaphase I of meiosis: 2 chromatids per chromosome.
- At anaphase II of meiosis: 1 chromatid per chromosome.

### Final Answer:
The number of chromatids in a chromosome at anaphase is **1** (for mitosis and meiosis II) and **2** (for meiosis I).

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