• Genes (DNA) are the cause; the inherited traits are the effect.
• Variation within a population (different alleles) is the raw material on which natural selection works. Without variation there is nothing to select.
• Artificial selection uses the same variation, but the human breeder decides which individuals reproduce.
• Genetic diseases show what can happen when a harmful recessive allele becomes homozygous; communities reduce this through awareness, screening and counselling, which also respects human differences and protects the health of future generations.
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Test yourself on this lesson

• The lesson’s question bank is split across the points above; each point has its own questions underneath.
• To work through the whole bank on one page: