AQA · GCSE · Combined Science

    Course version: 8464 · Version from Sept 2018

    Selective breeding: The characteristic can be chosen for usefulness or appearance:

    Selective breeding works because variation exists within a species, and humans decide which variants become parents of the next generation.

    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Selective breeding works because variation exists within a species, and humans decide which variants become parents of the next generation. A characteristic is chosen either for usefulness, such as higher milk yield in cattle, disease resistance in wheat or larger fruit size, or for appearance, such as flower colour in roses, feather colour in poultry or coat colour in dogs. The chosen parents are bred, and their offspring that show the desired characteristic most strongly are bred again. Repeating this over many generations increases the frequency of the chosen alleles in the population. The characteristic must be heritable, so selecting a feature caused only by environment, such as a plant grown with extra fertiliser, will not reliably pass it on.

    What earns the marks

    • Selective breeding requires inherited variation in the chosen characteristic within the population.
    • Usefulness examples include higher yield, disease resistance, hardiness or improved nutritional content.
    • Appearance examples include colour, size, shape or other physical features valued by breeders.
    • The chosen parents are bred together and the best offspring are selected to breed in the next generation.
    • Repeating selection over many generations increases the proportion of individuals showing the desired characteristic.
    • Only heritable characteristics respond to selection; environmentally caused features do not reliably pass to offspring.

    Common mistakes and how to put them right

    • Thinking any chosen feature will be inherited.

      Put it right by checking that the characteristic is controlled by genes and shows variation between individuals.

    • Confusing selective breeding with genetic engineering.

      Put it right by stating that selective breeding crosses existing organisms and does not directly transfer genes between species.

    • Assuming one round of breeding is enough.

      Put it right by explaining that many generations of selection are usually needed to change the population.

    • Classifying temperament as an appearance characteristic.

      Put it right: Temperament is behavioural, not physical appearance, so it is not an appearance example.

    Exam tips

    • Name the organism, the chosen characteristic and whether the reason is usefulness or appearance in your first sentence.
    • Use the phrase heritable variation to show the characteristic can be passed on.
    • Describe the cycle of selection and breeding rather than only stating the final outcome.

    Try the lesson

    The start of the Selective breeding: The characteristic can be chosen for usefulness or appearance: lesson, made from checked teaching notes for this specification point.

    Have a go first

    A farmer decides which animals will be used to breed the next generation of the herd. Which statement describes why the farmer chooses specific animals for selective breeding?

    Listen

    Selective breeding works because variation exists within a species, and humans decide which variants become parents of the next generation. A characteristic is chosen either for usefulness, such as higher milk yield in cattle, disease resistance in wheat or larger fruit size, or for appearance, such as flower colour in roses, feather colour in poultry or coat colour in dogs. The chosen parents are bred, and their offspring that show the desired characteristic most strongly are bred again. Repeating this over many generations increases the frequency of the chosen alleles in the population. The characteristic must be heritable, so selecting a feature caused only by environment, such as a plant grown with extra fertiliser, will not reliably pass it on. A strong answer earns marks for these points. Selective breeding requires inherited variation in the chosen characteristic within the population. Usefulness examples include higher yield, disease resistance, hardiness or improved nutritional content. Appearance examples include colour, size, shape or other physical features valued by breeders. The chosen parents are bred together and the best offspring are selected to breed in the next generation. A common slip: Thinking any chosen feature will be inherited. Instead, checking that the characteristic is controlled by genes and shows variation between individuals. Exam tip: Name the organism, the chosen characteristic and whether the reason is usefulness or appearance in your first sentence.

    See it

    A flowchart running from top to bottom. The first box says variation exists within a species and points to a box saying choose a characteristic. That box branches into two boxes: reason: usefulness, and reason: appearance. Both of these point to a box saying breed chosen parents. This leads to a box saying select offspring showing the characteristic most strongly, which leads to a box saying breed these offspring again. That leads to a box saying repeat over many generations, which finally leads to a box saying frequency of chosen alleles increases.
    It shows how a characteristic chosen for usefulness or appearance is passed through repeated selection and breeding over many generations.

    Key words

    Say what each word means before you turn the card.

    inherited variation

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    artificial selection

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    usefulness versus appearance

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    change in allele frequency over generations

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    See every definition
    inherited variation
    Differences within a species that are controlled by genes, so they can be passed on to offspring.
    artificial selection
    Humans decide which variants become parents of the next generation, choosing a characteristic for usefulness or appearance.
    usefulness versus appearance
    A characteristic is chosen either for usefulness or for appearance when deciding which variants become parents.
    change in allele frequency over generations
    Repeating selection over many generations increases the frequency of the chosen alleles in the population.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A flowchart running from top to bottom. The first box says variation exists within a species and points to a box saying choose a characteristic. That box branches into two boxes: reason: usefulness, and reason: appearance. Both of these point to a box saying breed chosen parents. This leads to a box saying select offspring showing the characteristic most strongly, which leads to a box saying breed these offspring again. That leads to a box saying repeat over many generations, which finally leads to a box saying frequency of chosen alleles increases.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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