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Practice · Biology · 2025 syllabus · D1.3

IB Biology D1.3 Mutation and gene editing: practice questions

4 exam-style questions on D1.3 Mutation and gene editing, SL and HL, 1 marked HL: 3 multiple choice and 1 short answer. Each one comes with the mark scheme, a model answer and the reasoning behind every mark. Free with your email.

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D1.3-01 · Paper 1A style · multiple choice · 1 mark

Mutations with least effect

Which mutation in the coding sequence of a gene is most likely to have no effect on the polypeptide produced? [1]

  1. Substitution of the third base of a codon in the middle of the sequence
  2. Substitution that turns an amino acid codon near the start into a stop codon
  3. Deletion of a single base near the start of the coding sequence
  4. Insertion of two bases in the middle of the coding sequence
Show the answer and the reasoning

Answer: A. A is correct. Because the code is degenerate, codons for the same amino acid often differ only in the third base, so a change there frequently leaves the amino acid unchanged (a silent mutation). B stops translation early, giving a short, usually useless polypeptide. C and D both shift the reading frame (the number of bases added or removed is not a multiple of three), changing every codon downstream.

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The 4 questions in D1.3

  1. D1.3-01 Mutations with least effectPaper 1A style · multiple choice · 1 mark
  2. D1.3-02 A substitution in the templatePaper 1A style · multiple choice · 1 mark
  3. D1.3-03 Guide RNA in CRISPRPaper 1A style · multiple choice · 1 mark · HL
  4. D1.3-04 An inserted basePaper 2 style · short answer · 6 marks

More of D Continuity and change

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Every Biology and Chemistry question here is original, written for practice in the style of the papers set since the 2025 syllabus, with invented data. Developed independently from the International Baccalaureate Organization, which has not endorsed it. Found a mistake? Email vytis@limeadmissions.com with the question id.