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, heart disease, alcoholism, and Alzheimer's. One thousand dollars will buy you your own genome readout, neatly 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 every one 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 that tell cells when and where to turn genes on or off.

In 1935, Ernest Hemingway was supposedly given Snow White, a six-toed cat who went on to father a line of similar offspring that still roam the writer's Florida estate. Scientists now know that the fault driving this profusion of digits lies in a tiny genetic control switch, miles away (in molecular terms) from the gene that "makes" toes. Researchers are discovering more about the myriad molecular switches that make sure genes are turned on at the right time and in the right place, and what happens when they don't work properly. This is allowing a four-dimensional picture of DNA to be built--a dynamic biological library, rather than static strings of code. Geneticist Kat Arney explores the intricacies of how, out of this seeming genetic chaos, life is created.