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Genes and wiring

Genes make the chemical signals that guide the axons to their targets. But the body's instruction manual only contains about 80,000 genes. Even though about half of these may be involved in making and connecting the brain, there aren't enough to specify each of the billions of connections needed. Instead, the signals get the axons to roughly the right place, and the remaining connections form as they are used - both before and after birth.

Every neurone in your brain may have up to 10,000 interconnections.
Every neurone in your brain may have up to 10,000 interconnections.
David Becker/Wellcome Photo Library

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