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

Options

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

Answer

To answer the question "Every chromosome (visible only in dividing cells) essentially has a," we need to identify the essential structure present in every chromosome during cell division.

### Step-by-Step Solution:

1. **Understanding Chromosomes**: Chromosomes are structures that become visible during cell division. They are formed from the coiling and condensing of chromatin fibers.

2. **Identifying Key Structures**: In the context of chromosomes, we need to focus on the essential components that are present in every chromosome. The options provided are:
- Secondary constriction
- Centromere
- RDNA
- Centrosome

3. **Defining the Centromere**: The centromere is a specific region of the chromosome that plays a crucial role during cell division. It is the point where two sister chromatids are joined together and is essential for the movement of chromosomes during mitosis and meiosis.

4. **Evaluating Other Options**:
- **Secondary constriction**: This is not present in all chromosomes and is specific to certain chromosomes.
- **RDNA**: This refers to ribosomal DNA, which is not a structure visible in all chromosomes.
- **Centrosome**: This is a structure involved in organizing microtubules but is not a part of the chromosome itself.

5. **Conclusion**: The only structure that is essential and present in every chromosome during cell division is the **centromere**.

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

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