What is the ratio of the number of chromatids, chromosomes, bivalents and centromeres respectively in a cell during metaphase-I?

Options

A. `1:2:2:1`
B. `4:2:2:1`
C. `4:2:1:2`
D. `2:1:2:1`

Answer

To find the ratio of the number of chromatids, chromosomes, bivalents, and centromeres in a cell during metaphase-I, we need to understand the definitions and characteristics of each component during this phase of meiosis.

### Step-by-Step Solution:

1. **Identify the Number of Chromatids**:
- During metaphase-I, each homologous chromosome pair consists of two sister chromatids. Since there are two homologous chromosomes (one from each parent), the total number of chromatids is:
\[ \text{Number of Chromatids} = 4 \text{ (2 chromatids per chromosome × 2 chromosomes)} \]

2. **Identify the Number of Chromosomes**:
- In metaphase-I, the homologous chromosomes align at the equatorial plate. Since there are two homologous chromosomes, the total number of chromosomes is:
\[ \text{Number of Chromosomes} = 2 \]

3. **Identify the Number of Bivalents**:
- A bivalent is formed by a pair of homologous chromosomes. Therefore, in metaphase-I, there is one bivalent formed by the two homologous chromosomes:
\[ \text{Number of Bivalents} = 1 \]

4. **Identify the Number of Centromeres**:
- Each chromosome has one centromere. Since there are two chromosomes, the total number of centromeres is:
\[ \text{Number of Centromeres} = 2 \]

5. **Compile the Ratios**:
- Now, we can compile the numbers we found:
- Number of Chromatids: 4
- Number of Chromosomes: 2
- Number of Bivalents: 1
- Number of Centromeres: 2

- Therefore, the ratio of the number of chromatids, chromosomes, bivalents, and centromeres is:
\[ \text{Ratio} = 4 : 2 : 1 : 2 \]

### Final Answer:
The ratio of the number of chromatids, chromosomes, bivalents, and centromeres during metaphase-I is **4 : 2 : 1 : 2**.