Authentic Classroom Explanation by IAS Monk

🦠 Q6. Adenoviruses vs Retroviruses

📌 Question
Consider the following statements:

1. Adenoviruses have single-stranded DNA genomes whereas retroviruses have double-stranded DNA genomes.
2. 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.