IB DP Biology- D1.3 Mutations and gene editing- IB Style Questions For HL Paper 1A -FA 2025

Question

A DNA sequence before and after a mutation is shown.

Before mutation 3′ TAC TCC TGC TTC 5′
After mutation 3′ TAC TGC TGC TTC 5′

The table contains mRNA codons and their associated amino acids.

mRNA codon	Amino acid
AUG	Met
AGG	Arg
ACG	Thr
AAG	Lys
UAC	Tyr
UCC	Ser
UGC	Cys
UUC	Phe

What would be the effect of this mutation on the translated polypeptide?

(A) Thr would replace Arg.
(B) Cys would replace Ser.
(C) There would be an extra Arg.
(D) There would be no change in the amino acid sequence.

▶️ Answer/Explanation

Before mutation, the mRNA transcribed from the DNA sequence 3′–TAC TCC TGC TTC–5′ would be 5′–AUG AGG ACG AAG–3′, coding for Met–Arg–Thr–Lys.
After mutation, the sequence becomes 3′–TAC TGC TGC TTC–5′, giving mRNA 5′–AUG ACG ACG AAG–3′, coding for Met–Thr–Thr–Lys.
Thus, Thr replaces Arg due to the base substitution changing the codon AGG to ACG.
✅ Answer: (A)

Question

What is the main purpose of performing a gene knockout?

A.  Increasing protein output by altering a gene
B.  Studying a gene’s role by disabling it so it cannot function
C.  Detecting a gene by modifying it to create a different protein
D.  Altering a gene in order to trigger programmed cell death

▶️ Answer/Explanation

A gene knockout involves intentionally inactivating a gene to observe what changes occur in the organism. This helps reveal the gene’s normal function by seeing what happens when it is absent.
✅ Answer: (B)

IB DP Biology- D1.3 Mutations and gene editing- IB Style Questions For HL Paper 1A -FA 2025

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