Which can be observed in an interphase nucleus under the light microscope :-

Options

A. Chromosomes
B. Nucleosomes
C. Centromere
D. Heterochromatin

Answer

### Step-by-Step Solution:

1. **Understanding Interphase**: Interphase is the phase of the cell cycle where the cell is not dividing. It consists of three sub-phases: G1 (Gap 1), S (Synthesis), and G2 (Gap 2). During interphase, the genetic material is in the form of chromatin, which is less condensed than chromosomes.

2. **Identifying Observations in Interphase**: Under a light microscope, we need to determine what structures can be observed in the nucleus during interphase.

3. **Analyzing Options**:
- **Option 1: Chromosomes**: Chromosomes are not visible during interphase because they are not condensed. They become visible during the mitotic phase (metaphase).
- **Option 2: Nucleosomes**: Nucleosomes, which consist of DNA wrapped around histone proteins, are too small to be seen under a light microscope.
- **Option 3: Centromere**: The centromere, which is the region where two sister chromatids are joined, is also not visible during interphase as it is part of the condensed chromosomes seen during mitosis.
- **Option 4: Heterochromatin**: Heterochromatin is a form of chromatin that is more condensed and can be observed under a light microscope. It is transcriptionally inactive and appears darker in staining.

4. **Conclusion**: The only structure that can be observed in an interphase nucleus under a light microscope is **heterochromatin**. Therefore, the correct answer is **Option 4: Heterochromatin**.