| One of the most obvious gross morphological differences among dogs of different breeds is the length of their hair. For the majority of registered dog breeds, the breed standard allows only one hair length. However, variable hair lengths are allowed by the standard for some breeds, such as collies, Border collies, dachshunds and St. Bernards. In other breeds, such as Pembroke Welsh Corgis, the occasional appearance of long-haired dogs (also called “fluffies” in this breed) has been a problem for breeders. It has recently been demonstrated in some dog breeds (e.g. Weimeraner, Pembroke Welsh Corgi, Border Collie and German Shepherd Dog that a missense mutation is associated with the hair-length differences among these breeds. Long-haired coat length is inherited a an autosomal recessiv trait, therefore dogs that are carriers of the long hair mutation will appear to be normal (short hair) themselves but will likely pass on the long-hair mutation 50% of the time. The DNA test allows to distinguish between 3 possible genotypes:
1. N/N clear (those having 2 copies of the normal short-hair allele [N]).
2. N/F carrier (those having 1 copy of the normal short-hair allele [N] and 1 copy of the long-hair mutation [F]).
3. F/F affected (those having 2 copies of the long-hair mutation [F]).
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Coat length in dogs 
