The language of genes has become common parlance. We know they make our eyes blue, our hair curly, and they control our risks of cancer, alcoholism, and Alzheimer's. One thousand dollars will buy you your own genome readout, stored on a USB stick. And advances in genetic medicine hold huge promise.

We've all heard of genes, but how do they actually work? There are six feet of DNA inside each of your cells; this encodes 20,000 or so genes, tangled into a mass of molecular spaghetti. This is the text of the cookbook of life, and hidden within these strands are the instructions...