NOR is located at

Options

A. Tip
B. Trabant
C. Secondary constriction
D. Primary constriction

Answer

To answer the question "NOR is located at," we need to understand the context of the term NOR and its relation to chromosome structure. Here’s a step-by-step solution:

### Step-by-Step Solution:

1. **Understanding NOR**: NOR stands for Nucleolar Organizer Region. It is a specific region on a chromosome that is associated with the formation of the nucleolus during interphase.

2. **Chromosome Structure**: Chromosomes have various structural features, including constrictions. These constrictions can be classified into primary constriction (centromere) and secondary constriction.

3. **Secondary Constriction**: The NOR is located at the secondary constriction of the chromosome. This is a specific area that is not involved in the primary function of the chromosome but plays a crucial role in the formation of the nucleolus.

4. **Identifying the Location**: The NOR is typically found at the tips of the chromosomes, specifically at the secondary constriction. This is where ribosomal RNA genes are located, which are essential for ribosome production.

5. **Conclusion**: Therefore, the correct answer to the question "NOR is located at" is at the secondary constriction of the chromosome.

### Final Answer:
NOR is located at the secondary constriction of the chromosome.