Question

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : HIV has a higher mutation rate.
Reason (R) : RNA genomes have much higher mutation rate.
In the light of the above statements, choose the most appropriate answer from the options given below :

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

DNA replication is highly accurate because DNA polymerases have a "backspace key" (3' to 5' exonuclease proofreading). RNA polymerases and Reverse Transcriptase generally lack this function, making RNA viruses (like HIV, Influenza, and SARS-CoV-2) mutate much faster than DNA viruses.

Answer 1

The Correct Option is A

Step 1: Concept:
This Assertion-Reason question relies on understanding viral genetics, specifically why certain viruses evolve rapidly, focusing on the Human Immunodeficiency Virus (HIV).

Step 2: Step-by-step Explanation:

• Evaluating Assertion (A): HIV is notorious in the medical field for its exceptionally high mutation rate. This rapid evolution allows it to quickly develop resistance to antiviral drugs and evade the host's immune system, which is why treating it requires a cocktail of multiple drugs (HAART) and why developing a vaccine has been so difficult. The assertion is absolutely correct.

• Evaluating Reason (R): HIV belongs to the retrovirus family, meaning its genetic material is encoded in RNA. When an RNA virus replicates, it uses enzymes (like RNA-dependent RNA polymerase or Reverse Transcriptase) that generally lack the rigorous exonuclease "proofreading" capabilities found in DNA polymerases. Consequently, transcription errors are not corrected, leading to a much higher basal mutation rate in RNA genomes compared to DNA genomes. Reason (R) is a correct scientific principle.

• Relationship: The fact that HIV possesses an RNA genome (and uses error-prone reverse transcriptase) is the direct biological cause of its extremely high mutation rate. Therefore, Reason (R) perfectly explains Assertion (A).

Step 3: Final Answer:
Both statements are correct, and the reason correctly explains the assertion. This corresponds to option (A).