The ratio of centromeres, kinetochores, DNA molecules in a metaphase chromosome

Options

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

Answer

To solve the question regarding the ratio of centromeres, kinetochores, and DNA molecules in a metaphase chromosome, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Metaphase Chromosome**:
- During metaphase, chromosomes are highly condensed and visible under a microscope. Each chromosome consists of two sister chromatids that are joined at a region called the centromere.

2. **Identifying the Components**:
- **Centromeres**: The centromere is the constricted region of a chromosome where the two sister chromatids are joined. In a metaphase chromosome, there is one centromere per chromosome.
- **Kinetochore**: The kinetochore is a protein structure that forms on the centromere during cell division. It is responsible for the attachment of the chromosome to the spindle fibers. Each chromosome has two kinetochores (one on each sister chromatid).
- **DNA Molecules**: Each sister chromatid contains one molecule of DNA. Therefore, in a metaphase chromosome, there are two DNA molecules (one for each sister chromatid).

3. **Counting the Components**:
- For a single metaphase chromosome:
- Centromeres: 1
- Kinetochores: 2 (one for each sister chromatid)
- DNA Molecules: 2 (one for each sister chromatid)

4. **Establishing the Ratio**:
- The ratio of centromeres to kinetochores to DNA molecules can be expressed as:
- Centromeres : Kinetochores : DNA Molecules = 1 : 2 : 2

5. **Final Answer**:
- Therefore, the ratio of centromeres, kinetochores, and DNA molecules in a metaphase chromosome is **1:2:2**.