Q.31 Determine the correctness or otherwise of the following Assertion (a) and the Reason (r).
Assertion: N-methyl-N′-nitro-N-nitrosoguanidine (NTG) is an effective chemical mutagen.
Reason: Mutations induced by NTG mainly are the GC → AT transitions.
(A) both (a) and (r) are true and (r) is the correct reason for (a)
(B) both (a) and (r) are true but (r) is not the correct reason for (a)
(C) (a) is true but (r) is false
(D) (a) is false but (r) is true
NTG (N-methyl-N′-nitro-N-nitrosoguanidine) is a potent chemical mutagen widely used in microbial genetics, but the reason given does not fully explain its effectiveness. Both the assertion and reason are true, yet the reason is not the primary basis for its effectiveness as a mutagen.
Option Analysis
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(A) Both true, (r) correct reason: Incorrect. While NTG induces GC → AT transitions via O6-guanine alkylation, its effectiveness stems from high mutagenesis frequency across multiple mutation types (transitions, transversions, frameshifts), not just one specific transition.
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(B) Both true, (r) not correct reason: Correct. NTG is highly effective due to rapid DNA alkylation and poor repair detection, producing diverse mutations beyond mainly GC → AT; the reason is true but not the core explanation.
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(C) (a) true, (r) false: Incorrect. NTG does predominantly cause GC → AT transitions through guanine modification, making (r) true.
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(D) (a) false, (r) true: Incorrect. NTG’s proven high mutation rates in bacteria, yeast, and fungi confirm it as an effective mutagen.
NTG mutagen, or N-methyl-N′-nitro-N-nitrosoguanidine, serves as a powerful chemical mutagen in biotechnology and genetics research. This SEO-optimized guide analyzes the assertion-reason question on NTG inducing GC → AT transitions, ideal for GATE BT exam prep and molecular biology students.
NTG Mechanism
NTG alkylates O6 of guanine and O4 of thymine, leading to GC → AT transitions during replication as modified bases mispair. It excels in bacteria and yeast, yielding up to 40% auxotrophs at low lethality doses.
Assertion-Reason Evaluation
The assertion holds true: NTG ranks among top chemical mutagens for its potency. The reason is accurate for primary transitions but overlooks broader effects like transversions, explaining why option (B) fits best.
Exam Relevance
In GATE Biotechnology 2011 Q31, this tests understanding of mutagen specificity versus overall efficacy. Key for biochem engineering and microbiology curricula.
