Question

Under which of the following conditions will there be no change in the reading frame of following mRNA?

5’AACAGCGGUGCUAUU3’

• A. Deletion of GGU from 7th, 8th, and 9th positions
• B. Insertion of G at 5th position
• C. Deletion of G from 5th position
• D. Insertion of A and G at 4th and 5th positions, respectively

Answer 1

The correct option is A

Deletion of GGU from 7th, 8th, and 9th positions

The correct option is A.

Explanation of correct option:

1. GGU deletion, i.e. three nucleotides has no effect on the reading frame.
2. Because each codon is made up of three consecutive nucleotides, deleting or inserting three or multiples of three nucleotides has no effect on the reading frame.
3. Frame-shift mutation occurs when one or two nucleotides are inserted or deleted, changing the entire reading frame.

Explanation of incorrect options:

Option B:

1. Insertion of G at 5th position will give this effect:
   AAC AGG CGG UCG UAU U
2. Leaving out U as one won't give the same reading frame.

Option C:

1. Deletion of G from the 5th position will give this effect:
   AAC ACG GUG CUA UU
2. Again Leaving UU as a pair of two also won't give the same reading frame.

Option D:

1. We count triplet formation and adding A and G at 4th and 5th positions won't give the same effect. It would become AAC AAG GCG GUG CUA UU.
2. Last UU is pair of two that's why this option is wrong.

Final answer: Deletion of GGU from 7th, 8th, and 9th positions is the condition for no change in mRNA.