Every chromosome (visible only in dividing cells) essentially has a

Options

A. Secondary constriction
B. Centromere
C. rDNA
D. Centrosome

Answer

To solve the question "Every chromosome (visible only in dividing cells) essentially has a", we need to analyze the options provided and understand the structure of chromosomes during cell division.

### Step-by-Step Solution:

1. **Understanding Chromosomes**:
- Chromosomes are structures within cells that contain DNA. They are only visible during cell division (mitosis or meiosis) when they condense and become distinct entities.

2. **Identifying Key Features of Chromosomes**:
- During cell division, chromosomes are made up of two identical halves called sister chromatids, which are joined together at a specific region.

3. **Defining the Centromere**:
- The region where the two sister chromatids are joined is called the centromere. This is a crucial part of the chromosome as it plays a vital role in the movement of chromosomes during cell division.

4. **Evaluating the Options**:
- **Option 1: Secondary constriction** - This is not a defining feature of all chromosomes.
- **Option 2: Centromere** - This is the correct answer, as every chromosome has a centromere that holds the chromatids together.
- **Option 3: Recombinant DNA** - This is not a structural feature of chromosomes.
- **Option 4: Centrosome** - This is involved in cell division but is not a part of the chromosome itself.

5. **Conclusion**:
- Based on the above analysis, the correct answer is **Option 2: Centromere**.

### Final Answer:
Every chromosome (visible only in dividing cells) essentially has a **centromere**.