GCSE Biology · AQA 8461 · Topic 4.6.2
Variation and evolution
Key points
- Variation is caused by genes, the environment, or both. Mutations happen all the time; most have no effect.
- Natural selection: there is variation, some individuals are better suited and survive to breed, and pass on their alleles.
- Selective breeding chooses parents with useful traits over many generations, but reduces variety and can cause inbreeding problems.
- Genetic engineering moves a gene from one organism into another, e.g. insulin made by bacteria, or GM crops resistant to pests. Enzymes cut out the gene and insert it into a vector such as a plasmid.
- Cloning: tissue culture, cuttings, embryo transplants and adult cell cloning (as with Dolly the sheep).
- A new species forms when populations become so different that they can no longer interbreed to make fertile offspring (speciation).
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Individuals of the same species differ from one another, and that variation is the raw material for evolution. This sub-topic explains natural selection and how humans now change organisms deliberately through breeding, genetic engineering…
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