During prophase 1 of meiosis homologous chromosomes pair with each other to form bivalents. A bivalent is an association of:

Options

A. two chromatids and one centromere
B. four chromatids and two centromere
C. two chromatids and two centromere
D. four chromatids and four centromere

Answer

To answer the question about what a bivalent is during prophase I of meiosis, we can break down the explanation step by step:

### Step-by-Step Solution:

1. **Understanding Prophase I of Meiosis**:
- During prophase I of meiosis, homologous chromosomes (the chromosomes that are similar in shape, size, and genetic content) come together and pair up.

2. **Formation of Bivalents**:
- The pairing of homologous chromosomes leads to the formation of structures known as bivalents (or tetrads). A bivalent consists of two homologous chromosomes that are aligned closely together.

3. **Composition of a Bivalent**:
- Each homologous chromosome is made up of two sister chromatids (the identical copies formed by DNA replication). Therefore, when two homologous chromosomes pair up, they collectively contain four sister chromatids.

4. **Counting Centromeres**:
- Each chromosome has one centromere. Since there are two homologous chromosomes in a bivalent, there are two centromeres present.

5. **Conclusion**:
- Therefore, a bivalent is an association of four chromatids and two centromeres.

### Final Answer:
A bivalent is an association of **four chromatids and two centromeres**.

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