Bivalent chromosomes align themselves at the equator during

Options

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

Answer

**Step-by-Step Solution:**

1. **Understanding Bivalent Chromosomes:**
- Bivalent chromosomes are formed during the zygotene stage of prophase I in meiosis. They consist of homologous chromosomes that come together and are held by a protein structure called the synaptonemal complex.

2. **Identifying the Stage of Meiosis:**
- The bivalent chromosomes are most clearly observed during the pachytene stage of prophase I of meiosis I. This is when crossing over occurs, leading to genetic variation.

3. **Alignment of Bivalent Chromosomes:**
- The alignment of bivalent chromosomes at the equatorial plane occurs during metaphase I of meiosis I. During this stage, spindle fibers attach to the centromeres of the bivalent chromosomes, pulling them towards the equator of the cell.

4. **Understanding the Structure:**
- Each bivalent chromosome consists of four chromatids (two sister chromatids from each homologous chromosome), which is why they are sometimes referred to as tetrads (bi- meaning two, and tetrad meaning four).

5. **Conclusion:**
- Therefore, the correct answer to the question is that bivalent chromosomes align themselves at the equator during metaphase I of meiosis I.

**Final Answer:**
Bivalent chromosomes align themselves at the equator during **metaphase I of meiosis I**.

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