Selective Breeding

    OCR
    GCSE

    Selective breeding involves the artificial selection of parents with desired phenotypic traits to produce offspring with enhanced characteristics. This iterative process, repeated over many generations, accumulates favourable alleles within a population to improve yield, disease resistance, or aesthetic qualities. While essential for modern agriculture and domestication, candidates must recognise the associated reduction in the gene pool. This loss of genetic variation increases the risk of inbreeding depression and susceptibility to new diseases or environmental shifts.

    0
    Objectives
    3
    Exam Tips
    4
    Pitfalls
    4
    Key Terms
    5
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating that parents with the desired characteristic are selected from the existing stock
    • Award 1 mark for describing the breeding of these selected parents together
    • Credit responses that specify selecting the offspring showing the best desired characteristics to breed for the next generation
    • Essential marking point: The process must be described as repeated over 'many generations' to establish the trait
    • For risks: Award credit for linking inbreeding to a reduced gene pool or increased chance of inheriting harmful recessive genetic defects

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You have correctly identified the parents to breed, but you must state that this process is repeated over many generations to gain the mark"
    • "Good application to the specific animal/plant in the question. Now, consider the potential health risks to the organism caused by inbreeding"
    • "You mentioned 'making the gene stronger' — be precise: we are selecting for specific alleles, which reduces overall genetic variation"
    • "Excellent link between inbreeding and disease susceptibility. To improve, specify that this is due to the accumulation of recessive alleles"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that parents with the desired characteristic are selected from the existing stock
    • Award 1 mark for describing the breeding of these selected parents together
    • Credit responses that specify selecting the offspring showing the best desired characteristics to breed for the next generation
    • Essential marking point: The process must be described as repeated over 'many generations' to establish the trait
    • For risks: Award credit for linking inbreeding to a reduced gene pool or increased chance of inheriting harmful recessive genetic defects

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When describing the process, use a bullet-point structure to ensure the sequence 'Select -> Breed -> Select Offspring -> Repeat' is clearly communicated
    • 💡In 'Evaluate' questions regarding risks, explicitly link 'inbreeding' to 'accumulation of harmful recessive alleles' or 'susceptibility to new diseases' for top-band marks
    • 💡Always reference the specific organism and trait mentioned in the question (e.g., 'cows with high milk yield') rather than writing a generic description

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Omitting the phrase 'over many generations', implying the evolutionary change occurs instantly in the first set of offspring
    • Confusing selective breeding with genetic engineering; candidates often describe inserting genes or modifying DNA rather than sexual reproduction
    • Using vague terminology such as 'breed the strong ones' without identifying the specific trait required by the question context (e.g., high milk yield or drought resistance)
    • Stating that selective breeding creates new traits, rather than selecting for existing variation within the population

    Key Terminology

    Essential terms to know

    Process of artificial selection
    Agricultural yield and disease resistance
    Inbreeding and reduced gene pool
    Accumulation of desired alleles

    Likely Command Words

    How questions on this topic are typically asked

    Describe
    Explain
    Suggest
    Evaluate
    Compare

    Ready to test yourself?

    Practice questions tailored to this topic