Frameshift Mutations and Reading Frames — NEET Biology
✅ Asked in NEET 2019Under which condition will there be no change in reading frame of the given mRNA? (NEET 2019) 5' AACAGCGGUGCUAUU 3'
Under which condition will there be no change in reading frame of the given mRNA? (NEET 2019) 5' AACAGCGGUGCUAUU 3'
Answer & NCERT explanation
Correct answer: A — Deletion of GGU from 7th–9th positions
Deletion of GGU (3 bases) from positions 7-9 will not change the reading frame because removing exactly 3 bases (one complete codon) maintains the triplet reading pattern. Other options involve single base insertions/deletions or two-base insertion, which cause frameshift mutations and alter the reading frame. Only when multiples of 3 bases are added or removed does the reading frame remain unchanged, as codons are triplets.
Read more NCERT concept on the PYQ
Insertion or deletion of three or its multiple bases insert or delete in one or multiple codon hence one or multiple amino acids, and reading frame remains unaltered from that point onwards.
NTA tests whether you understand that insertion or deletion of bases in multiples of three (3, 6, 9, etc.) do NOT cause frameshift mutations because they preserve the reading frame downstream. Students commonly mistake any insertion/deletion as causing a frameshift, but the key is the number of bases added or removed. If bases deleted or inserted are NOT multiples of three, the reading frame shifts and all subsequent codons change, producing non-functional proteins. Remember: multiples of 3 bases = normal amino acids affected but frame intact; non-multiples of 3 = frameshift occurs for all downstream codons.
What does NCERT say about Insertion or deletion three?
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