Which of the following viruses is capable of synthesizing RNA over RNA

Options

A. (a) HIV
B. (b) TMV
C. `(c) phi xx 174` phage
D. (d) tumour virus

Answer

To determine which virus is capable of synthesizing RNA over RNA, we can analyze the options provided step by step.

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for a virus that can synthesize RNA from RNA directly, without converting it to DNA first. This process is known as RNA replication.

2. **Analyzing Option A: HIV**:
- HIV (Human Immunodeficiency Virus) is a retrovirus.
- It has RNA as its genetic material but first converts this RNA into DNA using an enzyme called reverse transcriptase.
- After converting to DNA, it can then synthesize RNA and subsequently proteins.
- Therefore, HIV does not synthesize RNA directly from RNA; it first goes through a DNA stage.

3. **Analyzing Option B: TMV (Tobacco Mosaic Virus)**:
- TMV is classified as a ribovirus, which means it has RNA as its genetic material.
- TMV does not have reverse transcriptase; it directly replicates its RNA.
- The genomic RNA of TMV can serve as a template for synthesizing more RNA, which means it can synthesize RNA from RNA directly.

4. **Analyzing Option C**: (Assuming a generic DNA virus)
- If the option refers to a virus with DNA as its genetic material, it cannot synthesize RNA from RNA. DNA viruses typically need to transcribe their DNA into RNA first.

5. **Analyzing Option D: Tumor Viruses**:
- Similar to option C, if these viruses have DNA genomes, they also cannot synthesize RNA from RNA directly.

6. **Conclusion**:
- Based on the analysis, the only virus capable of synthesizing RNA over RNA directly is **TMV (Tobacco Mosaic Virus)**.

### Final Answer:
**B) TMV (Tobacco Mosaic Virus)**