Lesson 3.4.3.1

3.4.3.1 Gene and chromosome mutation Quiz: AQA Biology, Unit 4

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.4.3.1, Gene and chromosome mutation: 20 multiple choice questions for the AQA Biology (7402), Unit 4: Genetic information, variation and relationships, written with Revision Ninja.

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The 20 questions

  1. What is a gene mutation?

    • A change in the amino acid sequence of a protein caused by translation errors on the ribosome.
    • A change in the number of chromosomes that occurs only during fertilisation.
    • A change in the base sequence of DNA, such as a base substitution or base deletion.
    • A movement of a whole gene to a new locus on a different chromosome by crossing over.

  2. Which two types of gene mutation are named in the specification?

    • Base deletion and base substitution.
    • Base duplication and crossing over.
    • Chromosome fusion and translocation.
    • Independent segregation and random fertilisation.

  3. Gene mutations can arise spontaneously during which process?

    • Digestion of starch in the ileum.
    • Translation on the ribosome.
    • Osmosis across the cell membrane.
    • DNA replication.

  4. Why does a base substitution not always change the protein made from a gene?

    • The genetic code is non-overlapping, so a base change always creates a stop codon.
    • The base substitution is always removed by splicing before the mRNA leaves the nucleus.
    • The genetic code is degenerate, so the new triplet may still code for the same amino acid.
    • The genetic code is universal, so every base substitution is ignored by the ribosome.

  5. What is a mutagenic agent?

    • An agent, such as ionising radiation or certain chemicals, that increases the rate of gene mutation.
    • An enzyme that repairs damaged DNA and stops mutations from occurring during replication.
    • A type of tRNA that carries amino acids that are never used in the final protein.
    • A form of selection that removes all alleles that are not present in the population.

  6. Mutations in the number of chromosomes can arise spontaneously by which process?

    • Chromosome non-disjunction during meiosis.
    • Binary fission of a prokaryotic cell with a single circular chromosome.
    • Splicing of pre-mRNA to remove introns before translation.
    • Crossing over during prophase of mitosis in a body cell.

  7. Which description best matches a gene mutation involving base deletion?

    • A base is replaced by another base, with no change in any codon of the gene at all.
    • A whole chromosome is lost from the nucleus, which always leads to the death of the cell.
    • Extra bases are copied from another chromosome, which always makes the protein longer.
    • One or more bases are lost from the DNA base sequence, which can alter the codons that follow.

  8. A chromosome mutation involves a change in chromosome number. Which example is consistent with non-disjunction during meiosis?

    • A gamete with a single base substitution, which after fertilisation gives a cell with a stop codon.
    • A gamete with two different alleles of a gene, which after fertilisation gives a cell with four alleles.
    • A gamete with an extra copy of a chromosome, which after fertilisation gives a cell with three copies of that chromosome.
    • A gamete with a circular plasmid, which after fertilisation gives a cell with an extra chromosome.

  9. A cell has a diploid number of 2n = 46. What is the chromosome number of a gamete produced by a normal meiosis?

    • 11.5
    • 46
    • 23
    • 92

  10. A student says that all gene mutations are harmful to the organism. Evaluate this claim.

    • The claim is right, because mutations are never passed on to the next generation of an organism.
    • The claim is wrong, because many mutations are harmful but some can be neutral or beneficial in particular environments.
    • The claim is partly right, because mutations are harmful only when they occur in the nucleus.
    • The claim is right, because every mutation in the base sequence always stops the protein being made.

  11. A mutation changes a codon so that a different amino acid is made. What is the most likely effect on the protein?

    • The protein is always destroyed by lysozymes in the cytoplasm as soon as it is made.
    • The protein always becomes longer, because each mutation adds a new amino acid to the chain.
    • The protein may change shape or function, depending on the position and nature of the amino acid change.
    • The protein is always unchanged, because the genetic code is degenerate in every case.

  12. An experiment exposes bacteria to a mutagenic chemical and the mutation rate rises. Which conclusion is best supported?

    • The chemical acts as a mutagenic agent, increasing the rate of gene mutation in the bacteria.
    • The chemical changes the genetic code, so all codons now code for the same amino acid.
    • The chemical causes all bacteria to undergo non-disjunction during binary fission.
    • The chemical reduces the rate of mutation, because it inhibits DNA replication in all bacteria.

  13. A researcher counts the chromosomes of cells in an individual and finds 47 instead of 46. Which mutation is most likely?

    • A gene mutation in which one base has been substituted by another in one gene.
    • A chromosome mutation in which an extra chromosome is present, probably from non-disjunction during meiosis.
    • A change in the genetic code, which means one codon now codes for two amino acids.
    • A gene mutation in which a block of bases has been deleted from one gene.

  14. Why are mutations described as the source of new alleles in a population?

    • Random mutation of a gene can produce a new allele that differs from the existing alleles.
    • Mutations always produce identical copies of existing alleles, so no new alleles are formed.
    • Mutations occur only in gametes, so they cannot add new alleles to the population at all.
    • Mutations are removed from the population by splicing, so no new alleles can persist.

  15. Which statement best describes the effect of a base substitution in a gene?

    • The gene is copied into a plasmid, which always removes the base from the chromosome.
    • The gene moves to a new locus, which always stops the protein from being made at all.
    • Two bases are inserted into the gene, which always changes every amino acid after the insertion.
    • One base is replaced by another, which may or may not change the amino acid coded for.

  16. A DNA sequence loses one base in the middle of a gene. Which statement about the effect is correct?

    • The deletion has no effect, because the code is non-overlapping and so the reading frame is unchanged.
    • The codons after the deletion are shifted, which can change every amino acid that follows.
    • The deletion makes the gene longer, because the missing base is replaced by an extra amino acid.
    • Only the one amino acid that corresponds to the lost base is changed, and no others.

  17. Which statement compares gene mutation and chromosome mutation correctly?

    • A gene mutation changes the chromosome number, while a chromosome mutation changes one base in one gene.
    • A gene mutation changes the base sequence of one gene, while a chromosome mutation changes the chromosome number or structure.
    • A gene mutation occurs only in prokaryotes, while a chromosome mutation occurs only in eukaryotes.
    • A gene mutation and a chromosome mutation both change only the amino acid sequence of the protein.

  18. A researcher finds that a mutation changes an mRNA codon to a stop codon. What is the most likely effect?

    • Translation is unaffected, because stop codons are ignored by the ribosome in all cases.
    • Translation continues beyond the normal end, producing a longer polypeptide than normal.
    • Transcription starts again from the same position, producing two identical polypeptides.
    • Translation ends early, producing a shorter polypeptide than normal.

  19. A group of cells is exposed to radiation and the rate of mutation increases. What is the best description of the radiation?

    • A type of tRNA that carries amino acids to the ribosome during translation.
    • A selective agent that removes alleles from the population faster than normal.
    • A mutagenic agent that increases the rate at which gene mutations occur.
    • A form of chromosome mutation that always produces a cell with an extra chromosome.

  20. A mutation in a gene changes a codon but the amino acid is unchanged. Which term best describes the code that allows this?

    • Haploid
    • Non-overlapping
    • Universal
    • Degenerate

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