A single gene is known to cause long haired phenotypes in mammals. This gene is fibroblast growth factor 5 (FGF5). In dogs, all long haired phenotypes are inherited in a recessive manner and while the single known mutation in FGF5 explained most of the long hair phenotypes in dogs, it was not a good match in some breeds, namely the Afghan hound, Japanese Chin, Samoyed, Silky terrier and Yorkshire terrier. Recent research has located four (4) additional mutations in FGF5 that broadens our understanding of long hair in dogs and helps to explain remaining long hair phenotypes. These newly located mutations do not explain differences in medium and short coat types and for the sake of the study even Siberian Huskies were deemed to have a “short” coat, except for the very lengthiest coat type.
Researchers studied 268 dogs from 27 breeds and also seven wolves. Confirming that some long haired phenotypes were not explain by known mutations they resequenced FGF5. The sequence found no further mutations in American Eskimo, Dachshund, Havanese and Standard poodle breeds nor were new mutations found in shorthaired dogs of the Boston terrier, Collie, Entlebucher mountain dog and Pug. Further mutations were found however in Afghan Hounds, Samoyeds, Akitas, Siberian Huskies, and Eurasiers that helped to explain the long haired phenotypes in these breeds. Although, most of these breeds are fixed for the long haired phenotype a few such as Siberian Huskies are not although long hair does occur in the breed. This brings the total of known mutations in FGF5 that affect hair length in dogs to five. It also appears that at least some of these mutations can be combined in a heterozygous way to produce similar long haired phenotypes. This is similar to brown in dogs where any 2 of the three known allele for brown can be combined to produce a brown dog. This type of heterogeneity for alleles of the FGF5 gene was found in the Afghan Hound, Eurasier, and the Samoyed. Researchers did determine that these alleles are inherited independently, with one mutation coming from each of the dogs parents, rather than two mutations being inherited in a linked way from the same parent. The researchers found the previously discovered mutation of FGF5 to be present in the following breeds: Afghan hound, Akita, Alaskan malamute, shorthaired Dachshund, Dalmatian, Eurasier, German shepherd dog, German wirehaired pointer, Samoyed, Siberian husky, German pinscher and Shiba Inu. They also found that all seven of the wolves included in this study were either heterozygous or homozygous for the previously found mutation. Given the greater prevalence of the previously known mutation, researcher hypothesize that it is the most ancient of the FGF5 mutations in dogs.
Hopefully tests for these newly located mutations will soon be available to help breeders avoid the long haired phenotype in breeds where it is considered a fault and also to help breeders who wish to breed for the long haired phenotype do so consistently.
Dierks, C., Mömke, S., Philipp, U., & Distl, O. (2013). Allelic heterogeneity of FGF5 mutations causes the long-hair phenotype in dogs. Animal genetics, 425–431. doi:10.1111/age.12010