rDNA is present in

Options

A. NOR
B. Telomere
C. Centromere
D. Kinetochore.

Answer

To answer the question "rDNA is present in," we need to analyze the options provided and understand what rDNA (ribosomal DNA) is and where it is located.

### Step-by-Step Solution:

1. **Understanding rDNA**:
- rDNA stands for ribosomal DNA. It is a type of DNA that is responsible for coding ribosomal RNA (rRNA), which is a crucial component of ribosomes, the cellular machinery that synthesizes proteins.

2. **Identifying the Options**:
- The options given are:
- A) NOR (Nuclear Organization Region)
- B) Telomere
- C) Centromere
- D) Kinetochore

3. **Analyzing Each Option**:
- **A) NOR (Nuclear Organization Region)**:
- This region is specifically involved in the production of rRNA and is where rDNA is located. It plays a significant role in ribosome biogenesis.
- **B) Telomere**:
- Telomeres are the protective ends of chromosomes and do not contain rDNA.
- **C) Centromere**:
- The centromere is the part of a chromosome that links sister chromatids and is not associated with rDNA.
- **D) Kinetochore**:
- The kinetochore is a protein structure on the chromosome that is essential for chromosome movement during cell division, and it does not contain rDNA.

4. **Conclusion**:
- Based on the analysis, the correct answer is **A) NOR (Nuclear Organization Region)**, as this is the location where rDNA is present.

### Final Answer:
**rDNA is present in the Nuclear Organization Region (NOR).**