Variation, natural selection and evolution, adaptation, food chains and webs, nutrient cycles and human impact.
Variation
Variation is differences between individuals. Continuous variation (e.g. height) shows a range and is controlled by many genes plus the environment; discontinuous variation (e.g. blood group) falls into distinct categories controlled by genes only. Mutations — random changes in DNA — are the source of new alleles; their rate is increased by ionising radiation and some chemicals.
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