Noesis
Level 1 — RecognitionMutations & Gene Regulation

Mutations & Gene Regulation

⏱ 20 minutes30 marksprintable — key stays hidden on paper

Level 1: Recognition

Time limit: 20 minutes Total marks: 30

Section A — Multiple Choice (choose ONE answer) — 10 marks (1 each)

  1. A mutagen is best defined as: a) A gene that has changed b) An agent that increases the rate of mutation c) A protein that repairs DNA d) A type of chromosomal mutation

  2. Which point mutation involves the replacement of one base pair by another? a) Insertion b) Deletion c) Substitution d) Inversion

  3. A mutation that changes a codon but still codes for the same amino acid is called: a) Missense b) Nonsense c) Silent d) Frameshift

  4. A nonsense mutation results in: a) An amino acid substitution b) A premature stop codon c) No change to the protein d) A longer protein

  5. Sickle cell anaemia is caused by which type of mutation in the β-globin gene? a) Frameshift insertion b) Chromosomal translocation c) Single base substitution (missense) d) Nonsense mutation

  6. In the lac operon, lactose acts as: a) A repressor b) An inducer c) A corepressor d) An enhancer

  7. The trp operon is an example of a system that is: a) Inducible, switched ON by tryptophan b) Repressible, switched OFF by tryptophan c) Always constitutively active d) Controlled only by microRNA

  8. Addition of methyl groups to DNA (DNA methylation) usually: a) Increases gene expression b) Silences (reduces) gene expression c) Causes a frameshift d) Duplicates the gene

  9. A chromosomal mutation where a segment breaks off and reattaches in reverse orientation is a: a) Duplication b) Translocation c) Deletion d) Inversion

  10. microRNAs (miRNAs) regulate gene expression by: a) Binding DNA enhancers b) Binding complementary mRNA to block or degrade it c) Methylating histones d) Adding a poly-A tail

Section B — Matching — 6 marks (1 each)

  1. Match each mutation type (i–vi) to its description (A–F).
Term Description
(i) Frameshift A. Segment of chromosome present twice
(ii) Missense B. Insertion/deletion shifting the reading frame
(iii) Duplication C. Codon changed to a stop codon
(iv) Nonsense D. Codon changed so a different amino acid is coded
(v) Silent E. Occurs in body cells, not passed to offspring
(vi) Somatic mutation F. Base change with no effect on amino acid

Section C — True/False WITH Justification — 14 marks (2 each)

State True or False (1 mark) and give a one-line justification (1 mark).

  1. A germline mutation can be inherited by offspring, whereas a somatic mutation cannot.

  2. A single base insertion in a coding region has the same effect as a single base substitution.

  3. Transcription factors are proteins that bind DNA to help control the rate of transcription.

  4. Cystic fibrosis is caused by a mutation in a gene encoding a chloride ion channel protein (CFTR).

  5. In the lac operon, when lactose is absent the repressor binds the operator and transcription is blocked.

  6. Epigenetic changes such as histone modification alter the DNA base sequence.

  7. Gene regulation is important in development because different cell types express different genes despite having the same DNA.

Answer keyMark scheme & solutions

Section A (1 mark each)

  1. b — A mutagen is an environmental agent (chemical/radiation) that raises mutation frequency; it is not itself a gene or repair protein.
  2. c — Substitution swaps one base pair for another; insertion/deletion add/remove bases.
  3. c — Silent mutation: altered codon still specifies the same amino acid (redundancy of the genetic code).
  4. b — Nonsense mutation converts a sense codon into a premature stop codon, truncating the protein.
  5. c — GAG→GTG substitution gives Glu→Val (missense) in β-globin.
  6. b — Lactose (via allolactose) is the inducer that inactivates the repressor, switching the operon ON.
  7. b — trp operon is repressible: high tryptophan acts as corepressor, switching it OFF.
  8. b — DNA methylation typically represses/silences transcription.
  9. d — Reversed reattachment of a segment = inversion.
  10. b — miRNAs base-pair with complementary mRNA, blocking translation or triggering degradation (RNAi).

Section B (1 mark each)

  1. (i)–B, (ii)–D, (iii)–A, (iv)–C, (v)–F, (vi)–E Award 1 mark per correct pairing.

Section C (1 mark T/F + 1 mark justification)

  1. True. Germline mutations occur in gametes/gamete-forming cells and pass to offspring; somatic mutations occur in body cells and are not inherited.

  2. False. An insertion causes a frameshift altering all downstream codons, whereas a substitution changes only one codon — the effects differ greatly.

  3. True. Transcription factors bind DNA (promoters/enhancers) to activate or repress transcription.

  4. True. CF results from mutation of the CFTR gene encoding a chloride channel; commonly the ΔF508 deletion.

  5. True. No lactose → active repressor binds operator → RNA polymerase blocked → no transcription.

  6. False. Epigenetic modifications change gene expression without altering the underlying DNA base sequence.

  7. True. All cells share the same genome; differential gene regulation produces specialised cell types (differentiation).

Mark distribution

  • Section A: 10 × 1 = 10
  • Section B: 6 × 1 = 6
  • Section C: 7 × 2 = 14
  • Total = 30
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  {"claim":"Section A has 10 one-mark questions totalling 10 marks","code":"result = (10*1 == 10)"},
  {"claim":"Section B matching has 6 items totalling 6 marks","code":"result = (6*1 == 6)"},
  {"claim":"Section C has 7 T/F questions worth 2 marks each = 14","code":"result = (7*2 == 14)"},
  {"claim":"Overall total marks = 30","code":"secA=10*1; secB=6*1; secC=7*2; result = (secA+secB+secC == 30)"}
]