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Exam questions · Biology · Inheritance

Variation and Mutations

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

    State what is meant by continuous variation.

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    Model answer

    Variation in which a feature can have any value within a range.

    Mark scheme

    • Any value in a range — 1 mark
  2. 2 Give [2 marks]

    Give one example of discontinuous variation and one example of continuous variation in humans.

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    Model answer

    Discontinuous: eye colour, or blood group. Continuous: height, or weight.

    Mark scheme

    • Discontinuous example — 1 mark
    • Continuous example — 1 mark
  3. 3 Explain [3 marks]

    Explain why a bar chart with gaps is used to show the data for blood groups, but a histogram is used for heights.

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    Model answer

    Blood groups are discontinuous, as they fall into separate categories, so each is shown by a separate bar. Heights are continuous, as they can have any value in a range, so the bars touch in a histogram.

    Mark scheme

    • Blood group is discontinuous — 1 mark
    • Height is continuous — 1 mark
    • Gaps for categories, touching bars for a range — 1 mark
  4. 4 Calculate [3 marks]

    The masses of six mice were 21, 24, 22, 25, 22 and 26 g. Calculate the mean mass and state the mode.

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    Model answer

    21 + 24 + 22 + 25 + 22 + 26 = 140. 140 ÷ 6 = 23.3 g. The mode is 22 g.

    Mark scheme

    • Total of 140 — 1 mark
    • Mean 23.3 g — 1 mark
    • Mode 22 g — 1 mark
  5. 5 Describe [3 marks]

    Describe the effects that mutations can have on the phenotype of an organism.

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    Model answer

    Most mutations have no effect on the phenotype. Some mutations influence the phenotype, by changing a protein or the amount of it. A very few mutations determine the phenotype.

    Mark scheme

    • Most no effect — 1 mark
    • Some influence the phenotype — 1 mark
    • A very few determine the phenotype — 1 mark
  6. 6 Explain [6 marks]

    Explain how both genes and the environment are responsible for the differences in body mass between people, and explain where the genetic differences came from.

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    Model answer

    Body mass is an example of continuous variation, which is the result of many genes, and also the environment. A person's genes affect how they store fat and how fast they use energy, which sets a range for their mass. However, the environment is also important, because the person's diet and the amount of exercise they take change where in the range they end up. This is an interaction between the genome and the environment. The genetic differences between people are because they have different variants, or alleles, of genes. All variants arose from mutations, which are random changes in the DNA. Sexual reproduction then mixes the variants in each generation, so that each person has a different combination.

    Mark scheme

    • Body mass is continuous, from many genes — 1 mark
    • Genes set a range — 1 mark
    • Diet and exercise affect it — 1 mark
    • Interaction of the genome and the environment — 1 mark
    • Variants arose from mutations — 1 mark
    • Sexual reproduction mixes the variants — 1 mark

Quick check

  1. 1

    Which is an example of discontinuous variation?

    1. AHeight
    2. BWeight
    3. CEye colour
    4. DLeaf length
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    C: Eye colour

    Eye colour falls into distinct categories.

  2. 2

    Which is an example of continuous variation?

    1. AHeight
    2. BBlood group
    3. CEye colour
    4. DSex
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    A: Height

    Height can have any value in a range.

  3. 3

    Which type of chart is best for blood groups?

    1. AA histogram
    2. BA line graph
    3. CA scatter diagram
    4. DA bar chart
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    D: A bar chart

    A bar chart with gaps shows separate categories.

  4. 4

    What does all variation in the phenotype depend on?

    1. AOnly mutations
    2. BThe genome and the environment
    3. COnly the environment
    4. DOnly meiosis
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    B: The genome and the environment

    The genome, the environment, or both.

  5. 5

    What produces new variants?

    1. AFertilisation
    2. BMeiosis
    3. CMutations
    4. DRespiration
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    C: Mutations

    Mutations are the source of new variants.

  6. 6

    What effect do most mutations have on the phenotype?

    1. ANo effect
    2. BA harmful effect
    3. CA beneficial effect
    4. DThey always cause disease
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    A: No effect

    Most have no effect.

  7. 7

    Which of these is a mutagen?

    1. AWater
    2. BOxygen
    3. CGlucose
    4. DIonising radiation
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    D: Ionising radiation

    Ionising radiation increases the rate of mutation.

  8. 8

    The leaf lengths were 4, 5, 5, 6 and 10 cm. What is the mean?

    1. A5 cm
    2. B6 cm
    3. C10 cm
    4. D30 cm
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    B: 6 cm

    \((4 + 5 + 5 + 6 + 10) \div 5 = 6\) cm.

  9. 9

    Identical twins differ in body mass. What does this show?

    1. AThe twins have different genes
    2. BMass is not affected by the environment
    3. CThe environment affects body mass
    4. DMutations caused the difference
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    C: The environment affects body mass

    They have the same genome, so the difference must be caused by the environment.