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Gene variation

Although we all share the same genes, many have different versions, or alleles. They may only differ by one or two letters (base pairs) of their DNA code, but this might still affect the way a gene works. For example, different alleles of several genes affect hair colour, producing different shades. Alleles of some genes cause illness. Scientists can use special techniques to look at genes, and to spot differences between them.

Several genes affect hair colour.
Several genes affect hair colour.
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