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18. Variation and selection

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  1. 18.1 Variation

    1. 18.1.1Variation as differences between

      • Describe variation as differences between individuals of the same species

    2. 18.1.2Continuous variation results

      • State that continuous variation results in a range of phenotypes between two extremes; examples include body length and body mass

    3. 18.1.3Discontinuous variation results

      • State that discontinuous variation results in a limited number of phenotypes with no intermediates; examples include ABO blood groups, seed shape in peas and seed colour in peas

    4. 18.1.4Discontinuous variation is usually

      • State that discontinuous variation is usually caused by genes only and continuous variation is caused by both genes and the environment

    5. 18.1.5Examples of continuous

      • Investigate and describe examples of continuous and discontinuous variation

    6. 18.1.6Mutation as genetic change

      • Describe mutation as genetic change

    7. 18.1.7Mutation is the way in which new

      • State that mutation is the way in which new alleles are formed

    8. 18.1.8Ionising radiation and some chemicals

      • State that ionising radiation and some chemicals increase the rate of mutation

    9. 18.1.9Gene mutation as a random change

      • Describe gene mutation as a random change in the base sequence of DNA

    10. 18.1.10Mutation, meiosis, random mating

      • State that mutation, meiosis, random mating and random fertilisation are sources of genetic variation in populations

  2. 18.2 Adaptive features

    1. • Describe an adaptive feature as an inherited feature that helps an organism to survive and reproduce in its environment

    2. • Interpret images or other information about a species to describe its adaptive features

    3. • Explain the adaptive features of hydrophytes and xerophytes to their environments

  3. 18.3 Selection

    1. • Describe natural selection with reference to: (a) genetic variation within populations (b) production of many offspring (c) struggle for survival, including competition for resources (d) a greater chance of reproduction by individuals that are better adapted to the environment than others (e) these individuals pass on their alleles to the next generation

    2. • Describe selective breeding with reference to: (a) selection by humans of individuals with desirable features (b) crossing these individuals to produce the next generation (c) selection of offspring showing the desirable features

    3. • Outline how selective breeding by artificial selection is carried out over many generations to improve crop plants and domesticated animals and apply this to given contexts

    4. • Describe adaptation as the process, resulting from natural selection, by which populations become more suited to their environment over many generations

    5. • Describe the development of strains of antibiotic resistant bacteria as an example of natural selection

    6. • Outline the differences between natural and artificial selection