Q113 · Practice questionComplex familiar1 mark
QUESTION 113
A coding region gains one nucleotide and later loses one nucleotide downstream. Translation starts at the original start codon, and no new stop codon is introduced between the two changes. What happens to the reading frame downstream of both changes?
(A)
It remains displaced by two bases.
(B)
All codons in the entire gene must remain unchanged.
(C)
The original frame is restored, although intervening codons can change.
(D)
Every downstream codon becomes a stop codon.
WORKED SOLUTION
1 markAnswer C
Answer
C
Working
The net change in sequence length is zero, so the original downstream triplet grouping is restored. Codons between the insertion and deletion can still differ, and the encoded protein need not be unchanged.
Marking criteria
- Select C. [1 mark]
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
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