In meiosis I, a bivalent is an association of

Options

A. Four chromosomes and four centromeres
B. Four chromatids and two centromeres
C. Two chromatids and two centromeres
D. Two chromatids and one centromere

Answer

To answer the question "In meiosis I, a bivalent is an association of," we need to understand the structure of bivalents during meiosis.

### Step-by-Step Solution:

1. **Understanding Meiosis I**: Meiosis I is the first division in the process of meiosis, where homologous chromosomes are separated.

2. **Definition of Bivalent**: A bivalent refers to a pair of homologous chromosomes that are aligned together during meiosis. Each homologous chromosome consists of two sister chromatids.

3. **Chromatid and Centromere Structure**:
- Each chromosome in a bivalent is made up of two sister chromatids.
- Each pair of homologous chromosomes (bivalent) thus contains a total of four chromatids (2 from each chromosome).
- Each chromosome has one centromere, so a pair of homologous chromosomes (bivalent) will have two centromeres.

4. **Summarizing the Components**: Therefore, in a bivalent:
- There are 4 chromatids (2 from each of the 2 homologous chromosomes).
- There are 2 centromeres (1 from each of the 2 homologous chromosomes).

5. **Conclusion**: Based on the above analysis, the correct answer to the question is that a bivalent is an association of **4 chromatids and 2 centromeres**.

### Final Answer:
A bivalent is an association of **4 chromatids and 2 centromeres**.

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