Lesson 3.8.1.1

3.8.1.1 Gene mutations and their effects Quiz: AQA Biology, Unit 8

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.8.1.1, Gene mutations and their effects: 20 multiple choice questions for the AQA Biology (7402), Unit 8: The control of gene expression, written with Revision Ninja.

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The 20 questions

  1. Which of these is NOT a type of gene mutation?

    • Substitution
    • Inversion
    • Duplication
    • Crossing over

  2. A frame shift mutation is caused by:

    • Insertion of exactly three bases, which adds one complete extra codon and so shifts the reading frame of the whole gene
    • Inversion of a single base within the coding sequence, which swaps the codon around and always shifts the frame downstream
    • Substitution of one base for another, which changes a single codon and so always alters the amino acid in that position only
    • Insertion or deletion of a number of bases that is not a multiple of three

  3. What is a mutagenic agent?

    • An agent that prevents DNA from being replicated, so the cell cannot divide and the mutations stop accumulating in the population
    • An enzyme that joins amino acids together in a polypeptide chain during translation, which is needed for every protein made in the cell
    • An agent that increases the rate of gene mutation, such as ionising radiation
    • An agent that repairs damaged DNA by removing faulty bases, so that the rate of gene mutation falls in the cells it reaches

  4. The degenerate nature of the genetic code means:

    • Several different codons can code for the same amino acid
    • Every codon is read in both directions
    • Each codon codes for a different amino acid
    • Some codons are not read during translation

  5. Gene mutations are most often described as occurring:

    • Spontaneously, including during DNA replication
    • Only after cell division by cytoplasmic division
    • Only in cells that have stopped dividing
    • Only in response to a specific enzyme

  6. A mutation changes a codon but the amino acid stays the same. Which term describes this?

    • A frame shift mutation
    • A nonsense mutation
    • A silent mutation
    • A translocation mutation

  7. Sickle cell anaemia is caused by a substitution that changes one amino acid in haemoglobin. Which change occurs?

    • Lysine is replaced by alanine
    • Valine is replaced by glutamic acid
    • Glycine is replaced by serine
    • Glutamic acid is replaced by valine

  8. A codon CTT is changed to CTC by a mutation. Both codons code for leucine. What is the effect on the polypeptide?

    • Translation stops at this point
    • Two amino acids are removed from the polypeptide
    • A different amino acid is added to the polypeptide
    • No change in the amino acid, so the polypeptide is unchanged

  9. A codon GAG is changed to GTG by a mutation. What is the effect on the encoded amino acid?

    • Translation terminates at this codon
    • Glutamic acid is changed to lysine
    • Glutamic acid is unchanged
    • Glutamic acid is changed to valine

  10. A single base is deleted early in a gene's coding sequence. What is the most likely effect on the protein?

    • The protein is made in greater quantity, because the deleted base makes the mRNA more stable and so it is translated more often
    • A frame shift changes all downstream codons, so the polypeptide is likely to be non-functional
    • Only one amino acid changes and the protein is unaffected, because a single base deletion alters only the codon in which it lies
    • The mutation has no effect because it is near the start of the gene, where translation is always complete before any change occurs

  11. A single base is added to a 300-base coding region. Which statement is correct?

    • It causes a frame shift that changes all codons downstream of the mutation
    • It changes only the amino acid at the site of addition
    • It deletes a codon elsewhere in the gene
    • It has no effect because 300 bases is a multiple of three

  12. Which of these agents is mutagenic?

    • Dietary fibre
    • Ultraviolet radiation
    • Pure water
    • Vitamin C in normal amounts

  13. Why do most gene mutations not change an organism's phenotype?

    • The degenerate code, non-coding DNA and recessive alleles can mask or absorb the effect
    • Mutations only occur in cells that do not divide, so the mutations that matter for inheritance are removed from the gamete cells in meiosis
    • Mutations always cause large changes in every phenotype, so even a single base change in a gene produces a dramatic visible effect
    • All mutations are repaired before the gene is transcribed, so no change in the DNA sequence ever reaches the mRNA or the protein

  14. A translocation mutation involves which change?

    • A single base is added to the sequence
    • One base is replaced by another
    • A segment of DNA is moved to a different position
    • The whole chromosome is copied exactly once

  15. A duplication mutation has which effect?

    • Two genes are fused into one longer gene, so the product of the duplicated sequence is a single protein with two active sites
    • A section of DNA is copied, giving an extra copy of that sequence
    • A section of DNA is lost from the gene, so the sequence on either side of the gap is joined together and one copy of the code is missing
    • The sequence is reversed in direction within the gene, so the codons are read in the opposite order by the ribosome in every cell

  16. A deletion of one base is followed by an insertion of one base further downstream. What happens to the reading frame between the two mutations?

    • The frame is unchanged because the two mutations cancel out, so the gene is read exactly as it was before either mutation occurred
    • The frame is shifted permanently for the whole gene after the first mutation, so every codon from the start is misread in the same way
    • The frame is shifted only in the final codon of the gene, so the protein is affected only at its carboxyl terminus and nowhere else
    • The frame is shifted between the two mutations, but the frame is restored after the second mutation

  17. Mutations are random in the sense that they do not arise in response to need. Why are some mutations nonetheless beneficial?

    • Beneficial mutations are always produced by the same codon, so the same single base change is always the one that helps survival
    • Mutations occur only when the organism needs a new trait, so each beneficial change is produced by the cell in direct response to need
    • Those that improve survival in the environment are selected and their alleles increase in frequency
    • Beneficial mutations are always caused by genetic drift, which spreads useful alleles through the population

  18. A mutation rate of 1 in 10^6 per gene copy per generation is applied to 10^7 gene copies. How many mutations are expected per generation?

    • 1
    • 100
    • 10
    • 1000000

  19. Why would a change in amino acid at a protein's active site be more harmful than the same change on its surface?

    • Surface amino acids are never involved in protein function, so changes on the outside never affect the protein
    • The active site is made of DNA, which is not affected by mutation
    • A change at the active site can prevent the substrate from binding and so stops the protein working
    • Amino acids on the surface are always removed during translation, so a surface change is never retained in the finished protein molecule

  20. Which sequence best describes how a gene mutation changes a phenotype?

    • Phenotype change first, then base change in DNA, then codon change, then protein change, and finally the amino acid sequence altered
    • Protein shape change, then DNA base change, then mRNA codon change, then amino acid change, then altered phenotype in the organism
    • Base change in DNA, altered mRNA codon, altered amino acid sequence, altered protein shape and function, changed phenotype
    • Amino acid change first, then protein function change, then base change in DNA, then phenotype change, and finally codon change in mRNA

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