AQA · GCSE · Biology

    Course version: 8461 · Version from Sept 2018

    Selective breeding: They are bred together.

    Once parents with the desired characteristic have been chosen from a mixed population, they are bred together.

    Checked against the AQA 8461 specification (opens in a new tab) on .

    • Point 5 of 9
    • 2 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Once parents with the desired characteristic have been chosen from a mixed population, they are bred together. Their offspring inherit alleles from both parents, so some offspring may show the desired characteristic. The best offspring are then selected and bred together in the next generation. This cycle of selecting parents and breeding them is repeated over many generations. For example, a farmer breeds a high-yielding cow with a high-yielding bull, then selects the highest-yielding offspring to breed in the next round. Over time, the proportion of individuals with the desired characteristic increases. Breeding together selected parents is therefore the step that allows human choice to change the population.

    What earns the marks

    • Selected parents are mated or crossed so that they reproduce together.
    • Offspring inherit alleles from both selected parents.
    • Some offspring may show the desired characteristic and are selected for the next generation.
    • The cycle of selecting parents and breeding them is repeated over many generations.
    • Repeated breeding of selected individuals increases the proportion of the population with the desired characteristic.

    Common mistakes and how to put them right

    • Thinking breeding together selected parents guarantees all offspring will show the desired characteristic.

      Put it right by stating that inheritance involves chance, so only some offspring may show it.

    • Stopping after one generation.

      Put it right by explaining that the selection and breeding cycle must be repeated over many generations.

    • Breeding selected individuals with unselected ones.

      Put it right by stating that only individuals with the desired characteristic should be bred together.

    Exam tips

    • Describe the full cycle: choose parents, breed them, select the best offspring, and repeat.
    • Use the term 'offspring' and state that they inherit alleles from both parents.
    • When explaining improvement over time, refer to the increasing proportion of individuals with the desired characteristic.

    Try the lesson

    The start of the Selective breeding: They are bred together. lesson, made from checked teaching notes for this specification point.

    Have a go first

    A farmer wants to use selective breeding to produce a herd of cattle with a high milk yield. After selecting a cow with a high milk yield and a bull whose female relatives have high milk yields, what is the next step in the process?

    Listen

    Once parents with the desired characteristic have been chosen from a mixed population, they are bred together. Their offspring inherit alleles from both parents, so some offspring may show the desired characteristic. The best offspring are then selected and bred together in the next generation. This cycle of selecting parents and breeding them is repeated over many generations. For example, a farmer breeds a high-yielding cow with a high-yielding bull, then selects the highest-yielding offspring to breed in the next round. Over time, the proportion of individuals with the desired characteristic increases. Breeding together selected parents is therefore the step that allows human choice to change the population. A strong answer earns marks for these points. Selected parents are mated or crossed so that they reproduce together. Offspring inherit alleles from both selected parents. Some offspring may show the desired characteristic and are selected for the next generation. The cycle of selecting parents and breeding them is repeated over many generations. A common slip: Thinking breeding together selected parents guarantees all offspring will show the desired characteristic. Instead, stating that inheritance involves chance, so only some offspring may show it. Exam tip: Describe the full cycle: choose parents, breed them, select the best offspring, and repeat.

    See it

    A flowchart running from top to bottom. The first box says choose parents with the desired characteristic from a mixed population, and an arrow leads down to a box saying breed the selected parents together. An arrow leads down to a box saying offspring inherit alleles from both parents, then down to a box saying some offspring may show the desired characteristic, then down to a box saying select the best offspring. From that box an arrow loops back up to the breeding box, and another arrow leads down to a box saying repeat the cycle over many generations, which leads down to a final box saying proportion of individuals with the desired characteristic increases.
    It shows the repeated cycle of selecting parents with the desired characteristic, breeding them together, selecting the best offspring and repeating over many generations, so that the proportion with the desired characteristic increases.

    Key words

    Say what each word means before you turn the card.

    Offspring

    Try answering aloud or in your head before turning the card.

    Repeated selection over generations

    Try answering aloud or in your head before turning the card.

    See every definition
    Offspring
    The young produced when selected parents are bred together, which inherit alleles from both parents.
    Repeated selection over generations
    The cycle of selecting parents and breeding them, repeated over many generations.

    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 choose parents with the desired characteristic from a mixed population, and an arrow leads down to a box saying breed the selected parents together. An arrow leads down to a box saying offspring inherit alleles from both parents, then down to a box saying some offspring may show the desired characteristic, then down to a box saying select the best offspring. From that box an arrow loops back up to the breeding box, and another arrow leads down to a box saying repeat the cycle over many generations, which leads down to a final box saying proportion of individuals with the desired characteristic increases.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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