Lesson 6.1.1a

6.1.1a Gene mutations Quiz: OCR Biology, Unit 7

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 6.1.1a, Gene mutations: 20 multiple choice questions for the OCR Biology (H020), Unit 7: Genetics and evolution, written with Revision Ninja.

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The 20 questions

  1. What is the name for a gene mutation in which one nucleotide is replaced by another?

    • Substitution
    • Translocation
    • Crossing over
    • Non-disjunction

  2. Which type of gene mutation results in a frameshift that alters all subsequent downstream codons?

    • Base substitution
    • Silent mutation
    • Inversion mutation
    • Single nucleotide insertion

  3. What feature of the genetic code explains why silent mutations occur?

    • Non-overlapping nature
    • Degeneracy
    • Triplet nature
    • Universality

  4. Which type of codon is produced by a nonsense mutation?

    • Stop codon
    • Degenerate codon
    • Start codon
    • Sense codon

  5. Which amino acid replaces glutamic acid in sickle cell haemoglobin?

    • Leucine
    • Glycine
    • Alanine
    • Valine

  6. Which option is a physical mutagen?

    • Infrared radiation
    • Ionising radiation
    • Visible light
    • Radio waves

  7. During which cellular process do most spontaneous gene mutations occur?

    • DNA replication
    • Transcription
    • Cytokinesis
    • Translation

  8. The mRNA codon UAU mutates to the stop codon UAA. Which mutation type is this?

    • Nonsense mutation
    • Silent mutation
    • Frameshift mutation
    • Missense mutation

  9. Codon UUU mutates to UUC, both coding for phenylalanine. What type of mutation is this?

    • Silent mutation
    • Insertion mutation
    • Nonsense mutation
    • Missense mutation

  10. What is the direct result of a three-base deletion within an exon?

    • Complete frameshift
    • Premature stop codon
    • No effect
    • One amino acid lost

  11. What effect does deleting a single base pair from a gene cause?

    • Silent mutation
    • Duplication
    • Frameshift
    • Substitution

  12. A mutation causes a protein to fold incorrectly and lose its active site. How is this mutation best classified?

    • Silent
    • Beneficial
    • Harmful
    • Neutral

  13. Which condition is caused by a beneficial mutation in humans?

    • Huntington's disease
    • Cystic fibrosis
    • Lactase persistence
    • Sickle cell anaemia

  14. A gene of 3000 base pairs has a mutation rate of 1 in 10^6 per base per generation. Across 1000 copies of the gene, how many mutations are expected?

    • 3000
    • 0.3
    • 3
    • 30

  15. A missense mutation substitutes an amino acid with a chemically similar one. What is the effect?

    • Loss of function
    • Lethal effect
    • Neutral effect
    • Frameshift

  16. Why do mutations in non-coding DNA often have neutral effects?

    • No amino acid change
    • Halt transcription completely
    • Destroy the promoter
    • Always cause frameshifts

  17. How are the effects of mutations on organism fitness categorised?

    • Fast, slow, stopped
    • Lethal, silent, active
    • Harmful, neutral, beneficial
    • Dominant, recessive, codominant

  18. Why is a three-base insertion usually less damaging than a one-base insertion?

    • It adds a start codon
    • No frameshift occurs
    • It removes introns
    • It is always repaired

  19. What primary effect does a mutation in a gene promoter region have?

    • Alters transcription rate
    • Triggers instant apoptosis
    • Changes amino acid sequence
    • Causes a frameshift

  20. A gene has a mutation rate of 2 x 10^-6 per gene per generation. In a population of 500,000 individuals, each with one copy of the gene, how many new mutations are expected per generation?

    • 1
    • 10
    • 100
    • 0.1

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