Statement–I is false but Statement–II is true. A stop codon created by middle-gene mutation is a nonsense mutation, not frameshift; frameshift mutations arise from indels shifting the reading frame, though they often create premature stops.
Statement Analysis
Statement–I: False. Nonsense mutations substitute a codon for a stop codon (e.g., CAG→TAG), truncating proteins. Frameshift mutations (insertions/deletions not divisible by 3) alter the reading frame, changing all downstream codons—often leading to stops but defined by frame shift, not stop creation.
Statement–II: True. Single nucleotide indels (±1 bp, not multiples of 3) are point mutations (one site change) that cause frameshifts by disrupting triplet reading.
Option Breakdown
| Option | Explanation |
| Both true | Wrong: I false . |
| Both false | Wrong: II true . |
| I true, II false | Wrong: I false, II true . |
| I false, II true | Correct: Nonsense ≠ frameshift; point indels cause frameshift . |
Mutation middle gene stop codon frameshift confusion trips NEET aspirants—it’s nonsense mutation, while frameshift requires reading frame shift via indels.
Key Distinctions
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Nonsense: Point substitution creates stop (e.g., Trp→Stop in β-thalassemia).
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Frameshift: Indel shifts codons (e.g., -1 bp: ATG-CGT → AT-GCG-T…), garbling protein; may hit stop early.
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Overlap: Single bp indel (point mutation) causes frameshift, proving Statement II.
Exam Traps
Questions test definitions: “creates stop codon” = nonsense; “shifts reading frame” = frameshift. Cystic fibrosis (ΔF508 deletion) exemplifies frameshift.
