Nobody would mistake a human for a chimpanzee, yet we share more DNA than mice and rats do. How can that be? Advances in genomics are starting to unravel the mystery. Line up the genomes of humans and chimps side by side and they differ by little more than 1 per cent. That may not seem like much, but it equates to more than 30 million point mutations. Around 80 per cent of our 30,000 genes are affected, and although most have just one or two changes (Gene, vol 346, p 215), these can have dramatic effects.
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