Which type of coiling occurs in chromosomes ?

Options

A. Plectonemic
B. Paranemic
C. Orthostichous
D. Anorthospiral

Answer

To answer the question "Which type of coiling occurs in chromosomes?", we need to explore the different types of coiling that can occur in DNA and chromosomes. Here’s a step-by-step breakdown of the solution:

### Step-by-Step Solution:

1. **Understanding Chromosome Structure**:
- Chromosomes are made up of DNA that is tightly coiled and organized. This coiling is essential for the DNA to fit within the nucleus of a cell and to ensure proper segregation during cell division.

2. **Types of Coiling**:
- There are different types of coiling in DNA, primarily **plectonemic** and **paranemic** coiling.
- **Plectonemic Coiling**: In this type, the two strands of DNA (or chromatids) are coiled around each other tightly. This coiling is so tight that it requires a significant amount of force to unwind them. This type of coiling is typically observed during mitosis.
- **Paranemic Coiling**: In this type, the strands are coiled around each other loosely. This means that they can be unwound more easily compared to plectonemic coiling. Paranemic coiling is generally observed during meiosis.

3. **Identifying the Correct Coiling Type**:
- The question specifically asks about the type of coiling that occurs in chromosomes. Based on the definitions:
- Plectonemic coiling occurs during mitosis and is characterized by tight coiling.
- Paranemic coiling occurs during meiosis and is characterized by loose coiling.
- Since chromosomes are tightly coiled during mitosis, the correct answer to the question is **Plectonemic Coiling**.

4. **Conclusion**:
- The type of coiling that occurs in chromosomes is **Plectonemic**.

### Final Answer:
The type of coiling that occurs in chromosomes is **Plectonemic**.