The differences between the silky coat of a cocker spaniel, the wiry hair of a Scottish terrier and the soft curls of a poodle are caused by variations in only three genes, scientists have discovered.

A study of the canine genome has identified the genes that together account for the seven common styles of dog coat, which are present in about 90 per cent of pedigree breeds.

As well as offering insights into the evolution of the 209 distinct dog breeds, the findings have implications for understanding human genetics.

The researchers believe that similar techniques should illuminate human traits and diseases with similarly complex genetic roots, such as diabetes and cancer.

“What’s important for human health is the way we found the genes involved in dog coats and figured out how they work together, rather than the genes themselves,” said Elaine Ostrander, head of cancer genetics at the US National Human Genome Research Institute (NHGRI), who led the study.

“We think this approach will help pinpoint multiple genes involved in complex human conditions such as cancer, heart disease, diabetes and obesity. If we can decipher the genetic basis for a complex trait such as the dog’s coat, we believe that we can do it with complex diseases.”

The study, published in the journal Science, examined the DNA of more than 1,000 dogs from 80 breeds to search for genetic variations that might contribute to the three key traits that govern coat styles: length, growth pattern and curl.

They found that each of these traits is controlled largely by a single gene that comes in different variants.

A gene called RSPO2 controls the pattern in which hair grows, so that dogs with a particular version have wiry hair and moustaches and long facial details known to breeders as “furnishings”. Hair length and softness is governed by another gene called FGF2, while curl is affected by a gene called KRT71.

The combinations in which these genes are inherited then determine a dog’s overall look.

Dogs with short, straight hair, such as basset hounds and beagles, have none of the variant genes. Wire-haired dogs (which all have furnishings), such as Australian terriers, have a variant version of RSPO2 only. Dogs with long, soft hair, such as golden retrievers, have a variant version of FGF5 only.

Breeds such as the bearded collie, with long hair and furnishings, have variant versions of RSPO2 and FGF5. Breeds with wiry, curly hair, such as Airedale terriers, have variant versions of RSPO2 and KRT71. Breeds such as Irish water spaniels, with long, curly hair, have variant versions of KRT71 and FGF5.

Dogs with variant versions of all three genes, such as the bichon frisé, have long, curly hair and furnishings.

Some breeds, such as the Portuguese water dog and the dachshund, can have multiple coat varieties. Dachshunds can be wire-haired, long-haired or short-haired according to their genetic make-up. Wire-haired dachshunds have the RSPO2 variant, long-haired dachshunds have the FGF5 variant, while short-haired dachshunds have neither.

Some Portuguese water dogs, such as President Obama’s pet, Bo, have a variant KRT71 gene and long curls, while others lack it and have shorter, wavy hair.

Other aspects of dogs’ appearance are governed by different genes, many of which are already known. A genetic variant that explains the short legs of dachshunds and pekinese, for example, was identified by the same team last month. Dr Ostrander said: “When we put these genetic variants back together in different combinations, we found that we could create most of the coat varieties seen in what is among the most diverse species in the world — the dog.”

The study was conducted using a technique called the genome-wide association study, by which scientists look for genetic variants that are more common among individuals with particular traits. A similar approach has already identified genetic variations linked to more than 500 common diseases and traits in human beings.

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