Hair length is an important morphological trait that varies between different dog breeds. The fibroblast growth factor 5 (FGF5) is the only known gene leading to long-haired phenotype in mammals. Long hair is inherited as a simple recessive trait.
There are five known mutations in the FGF5 gene associated with long-hair phenotype in dogs: p.Cys95Phe, c.578C>T, c.559_560dupGG, g8193T>A and c.556_571del16. These all are now included in MyDogDNA 2016 test content. New test results of c.559_560dupGG, g8193T>A and c.556_571del16 variants are provided for dogs with MyDogDNA 2015.
The p.Cys95Phe mutation is completely concordant with long-hair phenotype in many dog breeds. However, it doesn’t explain all long-haired phenotypes.
Rare FGF5 mutations c.559_560dupGG and g8193T>A together with p.Cys95Phe seem to explain the long-haired phenotype at least in Afghan Hounds, long-haired Salukis and Chow Chows, and c.559_560dupGG and c.556_571del16 together with p.Cys95Phe in Eurasiers. In addition, both p.Cys96Phe and c.559_560dupGG variants seem to be present in Chinooks. The genetic variant c.578C>T seems to be present at least in Finnish Lapphunds, Australian Shepherd, Samoyeds, long-haired Akitas and possibly long-haired Siberian Huskies.
All long-hair associated mutations follow a recessive mode of inheritance. Any combination of these recessive alleles will produce a long-haired phenotype.
These five tested long coat variants explain a majority, but not all variation in coat length. This indicates that there are also other variants that partially influence coat length, e.g. in Yorkshire Terriers and Silky Terriers. Moreover, please note that your dog’s final coat appearance will also depend on other genetic variants, such as the ones determining curly vs. non-curly coat, and presence of furnishings (moustaches and eyebrows).
Online Mendelian Inheritance in Animals, OMIA (http://omia.angis.org.au/). Faculty of Veterinary Science, University of Sydney, May 2013; OMIA000439-9615.
Dierks C, Mömke S, Philipp U, Distl O. Allelic heterogeneity of FGF5 mutations causes the long-hair phenotype in dogs. Anim Genet :, 2013. Pubmed: 23384345.
Cadieu E, Neff MW, Quignon P, Walsh K, Chase K, Parker HG, Vonholdt BM, Rhue A, Boyko A, Byers A, Wong A, Mosher DS, Elkahloun AG, Spady TC, André C, Lark KG, Cargill M, Bustamante CD, Wayne RK, Ostrander EA. Coat variation in the domestic dog is governed by variants in three genes. Science. 326(5949):150-153 2009 Pubmed: 19713490.