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Mutations and Gene Editing · Paper 2 — Free Biology HL Practice Questions
1ChallengeSAQ-LTypes of mutations: Point, frameshift, chromosomal8 marksPaper 2~12 min
The CFTR gene encodes the CFTR chloride ion channel protein. Mutations in this gene cause cystic fibrosis. The wild-type CFTR protein is amino acids long.
A patient with severe cystic fibrosis has a single cytosine (C) nucleotide deleted from exon 10 of the CFTR gene. The wild-type mRNA sequence around this region is:
corresponding to the amino acid sequence: Lys – Asn – Ile – Ser – Phe – Asp – Glu.
The deletion removes the first nucleotide (U) of the UCC codon (Ser) from the mRNA.
(a)
State the type of mutation caused by this single-nucleotide deletion. [1 mark]
(b)
Determine the new mRNA sequence from the point of deletion onwards, and identify the first four amino acids produced from that point. Use the genetic code table from the IB Data Booklet. [3 marks]
(c)
Explain why this deletion is classified as a frameshift mutation and describe the likely effect on the length and function of the CFTR protein. [2 marks]
(d)
A second patient carries a point mutation that changes the UCC codon (Ser) to UCA (also Ser). Evaluate whether this point mutation would have a less severe effect on CFTR function than the frameshift mutation described above, justifying your answer with reference to protein structure and function. [2 marks]
Solutions
2ChallengeSAQ-LTypes of mutations: Point, frameshift, chromosomal8 marksPaper 2~12 min
A geneticist studies a population of Drosophila melanogaster examining mutations in a gene responsible for eye colour. The wild-type allele produces red eyes. Three mutant strains are isolated:
- Strain 1: A single base substitution in the coding region changes codon GAG (Glu) to GUG (Val).
- Strain 2: A deletion of a single adenine nucleotide in the coding region.
- Strain 3: A chromosomal translocation moves a segment of chromosome 2 containing the eye colour gene to chromosome 3.
All three strains show white eyes instead of red.
(a)
State which strain carries a frameshift mutation. [1 mark]
(b)
Describe the effect of each mutation the DNA sequence and the resulting protein for all three strains. [3 marks]
(c)
Explain why the chromosomal translocation in Strain 3 might have a different impact on offspring compared to the point mutation in Strain 1, even though both result in white eyes. [2 marks]
(d)
Evaluate the usefulness of frameshift mutations compared to point mutations for studying gene function in Drosophila, using evidence from all three strains. [2 marks]
Solutions
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