📘Q.6 IAS Prelims 2021 — GS | Science & Technology | Adenoviruses vs Retroviruses
Authentic Classroom Explanation by IAS Monk
🦠 Q6. Adenoviruses vs Retroviruses
📌 Question
Consider the following statements:
- Adenoviruses have single-stranded DNA genomes whereas retroviruses have double-stranded DNA genomes.
- Common cold is sometime caused by an adenovirus whereas AIDS is caused by a retrovirus.
Which of the statements given above is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
✅ Correct Answer: (b) 2 only
🧑🏫 Authentic Classroom Explanation by IAS Monk
From first principles to final option — the UPSC way.
🔬 Concept First
Viruses are classified based on:
- Type of genetic material (DNA / RNA, single or double stranded)
- Replication strategy
Confusing these is a classic UPSC trap.
🔍 Statement-wise Analysis
Statement 1:
Adenoviruses have single-stranded DNA and retroviruses have double-stranded DNA
❌ Incorrect
- Adenoviruses
- Possess double-stranded DNA (dsDNA) genomes
- Non-enveloped, icosahedral viruses
- Retroviruses
- Carry single-stranded RNA, not DNA
- Use reverse transcriptase to convert RNA → DNA inside host cell
👉 Hence, statement 1 is factually wrong on both counts.
Statement 2:
Common cold is sometimes caused by an adenovirus whereas AIDS is caused by a retrovirus
✔️ Correct
- Adenoviruses cause:
- Common cold
- Conjunctivitis
- Bronchitis, pneumonia
- AIDS is caused by HIV, a retrovirus
🔍 Curiosity Raiser
Did you know?
Retroviruses work “backwards” — they first convert RNA into DNA and then permanently integrate into the host genome.
🧠 Enrichment Notes (UPSC Lens)
- Adenovirus:
- dsDNA virus
- Widely used as vaccine vectors and gene therapy tools
- Retrovirus (HIV):
- ssRNA virus
- Uses reverse transcription
- Integration into host DNA makes it difficult to eradicate
- Common UPSC Trap:
- Assuming all DNA viruses are single-stranded (❌)
- Forgetting that retroviruses are RNA viruses
- Exam Value:
- Tests precision in biological classification
🪶 IAS Monk Closing Whisper
In biology, direction matters — especially when information flows backwards.