Under which of the following conditions will there be no change in the reading frame of following mRNA? 5'AACAGCGGUGCUAUU3'
Answer: (D) Deletion of GGU from 7th, 8th and 9th positions. Answer: (D) Deletion of GGU from 7th, 8th and 9th positions.
- A.Insertion of G at 5th position
- B.Deletion of G from 5th position
- C.Insertion of A and G at 4th and 5th positions respectively
- D.Deletion of GGU from 7th, 8th and 9th positions✓
Correct Answer
(D) Deletion of GGU from 7th, 8th and 9th positions
Solution & Explanation
Answer: (D) Deletion of GGU from 7th, 8th and 9th positions. The reading frame is read in contiguous triplets, so only insertion or deletion of bases in multiples of three preserves the frame; deleting the three bases GGU removes exactly one codon and leaves the downstream frame unaltered, whereas inserting or deleting one or two bases causes a frameshift. NCERT Ch 5, p.98, lines 3-6: "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."