OpenRevise

Exam questions · Biology · Reproduction, Meiosis and Variation

Mutations and Genetic Variation

  • 6 exam questions
  • 19 marks
  • 9 quick checks
  1. 1 State [1 mark]

    State what is meant by a mutation.

    Show answerHide answer

    Model answer

    A random change in the sequence of bases in DNA.

    Mark scheme

    • Change in the DNA base sequence — 1 mark
  2. 2 State [2 marks]

    State two factors that increase the rate of mutation.

    Show answerHide answer

    Model answer

    Any two from: ionising radiation such as X-rays or gamma rays, ultraviolet light, certain chemicals such as those in tobacco smoke.

    Mark scheme

    • First factor — 1 mark
    • Second factor — 1 mark
  3. 3 Explain [3 marks]

    Explain why most mutations have no effect on the phenotype.

    Show answerHide answer

    Model answer

    Most of the DNA of an organism is non-coding, so a mutation there does not change a protein. Also, different triplets can code for the same amino acid, so a change to a base may not change the amino acid. The protein is then the same, and the phenotype does not change.

    Mark scheme

    • Much DNA is non-coding — 1 mark
    • Different triplets can code for the same amino acid — 1 mark
    • So the protein is unchanged — 1 mark
  4. 4 Explain [3 marks]

    A mutation occurs in a skin cell, and another in a sperm cell. Explain which mutation could be inherited by a child.

    Show answerHide answer

    Model answer

    The mutation in the sperm cell could be inherited. The sperm fuses with an egg at fertilisation, so the mutation would be in every cell of the child. A mutation in a skin cell is not in the gametes, so it cannot be passed on.

    Mark scheme

    • Sperm cell mutation — 1 mark
    • Present in the zygote and every cell of the child — 1 mark
    • Skin cell mutation is not in the gametes — 1 mark
  5. 5 Explain [4 marks]

    Explain how a mutation in a bacterium can result in a whole population becoming resistant to an antibiotic.

    Show answerHide answer

    Model answer

    A mutation can give one bacterium resistance to the antibiotic. When the antibiotic is used, the non-resistant bacteria are killed, but the resistant one survives. It reproduces and passes the allele to its offspring, so over time the population is made up of resistant bacteria.

    Mark scheme

    • Mutation gives resistance — 1 mark
    • Non-resistant bacteria are killed — 1 mark
    • Resistant bacterium survives and reproduces — 1 mark
    • Allele passed on, so the population becomes resistant — 1 mark
  6. 6 Explain [6 marks]

    Explain why there is usually extensive genetic variation within a population, and why this is important for the species.

    Show answerHide answer

    Model answer

    New alleles are produced by mutations, which occur at random and have been happening over many generations, so the population has many different alleles. Sexual reproduction mixes these alleles in new combinations in each generation, through meiosis and random fertilisation, so each individual is different. Variation is important because if the environment changes or a new disease appears, some individuals will have features that help them survive. They can then reproduce and pass on their alleles, so the species can survive and evolve by natural selection.

    Mark scheme

    • Mutations produce new alleles — 1 mark
    • Over many generations — 1 mark
    • Sexual reproduction mixes them in new combinations — 1 mark
    • Individuals are different — 1 mark
    • Some may survive a change or disease — 1 mark
    • Natural selection / evolution — 1 mark

Quick check

  1. 1

    What is a mutation?

    1. AA change in the number of chromosomes only
    2. BA random change in DNA
    3. CA type of cell division
    4. DA feature gained during life
    Show answerHide answer

    B: A random change in DNA

    A mutation is a random change in the base sequence of DNA.

  2. 2

    Which of these can increase the rate of mutation?

    1. ADrinking water
    2. BEating protein
    3. CExercising
    4. DX-rays
    Show answerHide answer

    D: X-rays

    Ionising radiation, such as X-rays and UV light, can damage DNA and cause mutations.

  3. 3

    Most mutations have...

    1. ANo effect on the phenotype
    2. BA large effect
    3. CA beneficial effect
    4. DA lethal effect
    Show answerHide answer

    A: No effect on the phenotype

    Most mutations have no effect on the phenotype.

  4. 4

    Which mutation can be passed on to a child?

    1. AOne in a skin cell
    2. BOne in a liver cell
    3. COne in an egg cell
    4. DOne in a muscle cell
    Show answerHide answer

    C: One in an egg cell

    A mutation in a gamete is present in the zygote, so it can be inherited.

  5. 5

    Where do new alleles come from?

    1. AMeiosis
    2. BMutation
    3. CFertilisation
    4. DMitosis
    Show answerHide answer

    B: Mutation

    New alleles arise from mutations. Meiosis only reshuffles existing alleles.

  6. 6

    Why can a mutation in a gene have no effect on the protein?

    1. AGenes do not make proteins
    2. BThe DNA is not copied
    3. CMutations never happen in genes
    4. DDifferent triplets can code for the same amino acid
    Show answerHide answer

    D: Different triplets can code for the same amino acid

    Several different triplets code for the same amino acid, so the amino acid may not change.

  7. 7

    Which statement about mutations is correct?

    1. AThey are always harmful
    2. BThey are always beneficial
    3. CThey happen at random
    4. DThey only happen in plants
    Show answerHide answer

    C: They happen at random

    Mutations are random changes that occur spontaneously, and they happen at a low rate.

  8. 8

    Why is variation in a population important?

    1. ASome individuals may survive a change in the environment
    2. BIt makes all individuals identical
    3. CIt stops evolution
    4. DIt prevents mutations
    Show answerHide answer

    A: Some individuals may survive a change in the environment

    If conditions change, some individuals may survive because of their alleles, so the species can survive.

  9. 9

    A mutation in a bacterium gives it resistance to an antibiotic. Why does this affect the whole population over time?

    1. AThe mutation spreads through the air
    2. BThe resistant bacteria survive and reproduce
    3. CThe antibiotic changes the DNA of all bacteria
    4. DThe non-resistant bacteria change
    Show answerHide answer

    B: The resistant bacteria survive and reproduce

    When the antibiotic is used, the resistant bacterium survives and reproduces, passing on the allele, so the population becomes resistant.