You can't judge a book by its cover. But you can judge a dog by its coat. You can even read right through to its genes. Because a study in the August 27th online issue of Science shows that just three key genes govern the length and texture of dog fur. Domestic dogs come in a stunning variety of shapes and sizes, and different breeds wear different coats. They can have short hair or long hair, or fur that's straight, wavy, curly, wiry or smooth. To find the genes suitable for this furry rainbow, scientists scanned the DNA of a thousand individual dogs from 80 different breeds. And they found that every coat's appearance boils down to three simple traits: length, curl and texture. And that each of these traits is controlled by just one gene. So, a long-haired Golden retriever has one variant of a gene called FGF5, whereas a short-haired lab has another. By mixing and matching variants of these three genes, you get everything from a curly-haired poodle to a wire-haired Scottie with bushy eyebrows and a droopy moustache.