The genetics of dog hair colour is much more complicated than most people might think. There are many different genes, each themselves with sometimes three or four alleles, whose combination leads to the hundreds if not thousands of different coat varieties seen in canids both domestic and wild. Many people tend to think of genetics as working in the traditional Mendelian fashion of basic dominance and recessiveness of genes controlled by a single allele (say A/a), but dog hair colour is one of many examples where the answer is not that simple. The introduction of more than two alleles whose dominance over one another varies leads to many more possible combinations of traits and is why the pattern, colour, length and curliness of dog hair varies so widely across the family Canidae. One gene that plays a key role in coat colour is the agouti gene that encodes for a signalling molecule which disrupts the pathway in fur melanocytes (specialized pigment-producing cells) that leads to eumelanin production, these being darker brown and black pigment molecules. As a result, dogs that express the aguoti gene at high levels instead produce lighter phaeomelanin pigments that result in yellow, gold and even red coat colours. It's still not that simple however because the agouti gene has four alleles (a, aw ,at , ay ) each leading to varying levels of expression and different patterns of light and dark colours seen across the Canidae family.