Assertion (A): Viruses having RNA genome and having shorter life span mutate and evolve faster.
Reason (R): RNA being unstable, mutates at a faster rate.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both (A) and (R) are true and (R) is the correct explanation of (A).
Both DNA and RNA can mutate, but they do not change at the same speed. RNA is less stable than DNA: the 2′-OH group in every nucleotide makes it reactive and easily degraded.
Assertion (A): Viruses having RNA genome and having shorter life span mutate and evolve faster. — True. NCERT states this for RNA viruses.
Reason (R): RNA being unstable, mutates at a faster rate. — True. Being chemically unstable, RNA changes more often than DNA.
A is about RNA viruses evolving fast. R is about the property of their genetic material, RNA, that makes it change quickly.
Why R explains A? A virus whose genome is RNA carries a genetic material that mutates at a faster rate. More mutations in each generation, together with a short life span, mean new variants appear quickly, so such viruses evolve faster. NCERT links the two with “Consequently”, so R is the correct explanation of A.
NCERT Extract:
Properties of Genetic Material (DNA versus RNA) – “… Therefore, DNA chemically is less reactive and structurally more stable when compared to RNA. Therefore, among the two nucleic acids, the DNA is a better genetic material. … Both DNA and RNA are able to mutate. In fact, RNA being unstable, mutate at a faster rate. Consequently, viruses having RNA genome and having shorter life span mutate and evolve faster.”