Circular DNA occurs in

Options

A. Bacteria only
B. Bacteria and chloroplasts
C. All viruses
D. Bacteria, chloroplasts and mitochondria

Answer

**Step-by-Step Solution:**

1. **Understanding Circular DNA**: Circular DNA is a type of DNA molecule that forms a closed loop. It is commonly found in prokaryotes, such as bacteria, and in certain organelles of eukaryotic cells.

2. **Identifying Organisms with Circular DNA**:
- **Bacteria**: Most bacteria possess circular DNA as their genetic material. This is a defining characteristic of prokaryotic organisms.
- **Chloroplasts and Mitochondria**: These are organelles found in eukaryotic cells. Both chloroplasts (found in plant cells) and mitochondria (found in all eukaryotic cells) contain their own DNA, which is also circular. This is due to the endosymbiotic theory, which suggests that these organelles originated from free-living bacteria.

3. **Evaluating the Options**:
- **Option A: Bacteria only** - This is incorrect because chloroplasts and mitochondria also contain circular DNA.
- **Option B: Bacteria and chloroplasts** - This is partially correct but misses mitochondria, which also has circular DNA.
- **Option C: All viruses** - This is incorrect as viruses can have either circular or linear DNA, and not all viruses contain circular DNA.
- **Option D: Bacteria, chloroplasts, and mitochondria** - This is the correct answer as it includes all entities known to contain circular DNA.

4. **Conclusion**: The correct answer to the question "Circular DNA occurs in" is **bacteria, chloroplasts, and mitochondria**.

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