4. The frame shift mutation is induced by-
(1) Nitrous oxide (2) Acradines
(3) EMS (4) UV rays
Frame shift mutations occur due to insertion or deletion of nucleotides not in multiples of three, altering the reading frame of the genetic code. In the given MCQ, the correct answer is (2) Acridines, as these intercalating agents specifically induce frame shift mutations by slipping between DNA base pairs during replication.
Option Analysis
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(1) Nitrous oxide: This chemical mutagen causes base substitution mutations, such as deamination of bases leading to transitions (e.g., A:T to G:C), but does not insert or delete nucleotides for frame shifts.
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(2) Acridines: Correct choice; these planar molecules like proflavine intercalate into DNA, causing addition or deletion of bases during replication, resulting in frame shift mutations.
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(3) EMS (Ethyl Methanesulfonate): An alkylating agent that primarily induces point mutations by adding ethyl groups to guanine, leading to base mispairing, not frame shifts.
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(4) UV rays: These cause pyrimidine dimers (e.g., CPDs or 6-4PPs), typically resulting in C>T transitions after repair, rather than insertions/deletions for frame shifts.
Mechanism of Frame Shift Mutations
Acridines bind to DNA via intercalation, distorting the helix and promoting polymerase slippage, which adds or removes a single base. This shifts the codon reading frame downstream, often producing non-functional proteins. Such mutations are common in prokaryotes and used in genetic studies like Ames test variants.
