22. 2- Aminopurine induces mutation by
(1) Base pair change. (2) Frameshift
(3) Duplication (4) Deletion
2-Aminopurine (2AP), an adenine base analog, primarily induces mutations through base pair changes, specifically transition mutations like A:T to G:C, by mispairing with cytosine during DNA replication. This makes option (1) Base pair change the correct answer for the question. In CSIR NET Life Sciences exams, recognizing 2AP’s role as a transition mutagen is key for genetics sections.
Option Explanations
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(1) Base pair change: Correct. 2AP incorporates opposite thymine but can tautomerize or mispair with cytosine, leading to purine-purine mismatches resolved as transitions during replication.
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(2) Frameshift: Incorrect. Frameshifts result from insertions or deletions shifting the reading frame; 2AP mainly causes substitutions, not these, unlike intercalators like proflavine.
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(3) Duplication: Incorrect. Duplications involve repeated segments; 2AP does not promote this but targets single base substitutions via mispairing.
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(4) Deletion: Incorrect. Deletions remove bases; 2AP’s primary mechanism is base substitution, though minor indirect effects exist in some systems.
Mechanism of 2-Aminopurine Mutagenesis
2AP mimics adenine, pairing normally with thymine, but shifts to pair with cytosine via wobble, protonation, or tautomerism, creating A:T → G:C transitions. High dCTP levels enhance mispairing, as seen in cell studies. While minor frameshifts occur indirectly via mismatch repair saturation, transitions dominate. This mispairing model explains its specificity in bacterial and eukaryotic systems.
