The Fédération Cynologique Internationale is, as its name says, an association, a combination of ninety-one national canine organisations, defending common values, sometimes defending their own values, having however, a constant interest in mind : the DOG.

The FCI has to deal with, sometimes, 91 different points of views and each FCI member, in its turn, has to deal with a number of standpoints which is equal to the number of breeders/members affiliated to them in their country. It is therefore easy to figure out the multiplicity and the diversity of opinions with which we, FCI, have to deal daily.

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Y. De Clercq
FCI Executive Director
Alleles that govern dog coat variations

Until just a few years ago, there was little scientific data available on the genes that determine the heredity of coat traits in dogs. Lately, a French-American research team performed DNA-specific variance studies of about a thousand dogs from 80 breeds. The research was published in an article entitled “Coat variation in the Domestic Dog is Governed by Variants in Three Genes” (Cadieu et al.-2009 - Science).

The team identified three main alleles that govern the traits of the canine coat. Neither the “grey wolf” – the ancestor of the modern dog – nor the “short-haired” dogs feature these three alleles. This indicates that short-haired dogs carry ancestral alleles only. Combinations of the alleles of these three genes give rise to most of the many coat variations in dogs. Let us take them one by one. The symbols shown were borrowed from the latest articles published in this field (G.S. Barsh - 2012).

1. The gene for “hair length”

The FGF5 gene, located on chromosome 32, determines the length – long/short – of the hair. The “long hair” allele was observed in most long-haired dogs. An extended growth phase results in a longer coat. This confirms that the “long hair” allele displays a recessive mode of inheritance compared with the “short hair” allele. The length, for its part, may vary between individuals, and between breeds.

Across all breeds, the recessive allele was found in 91% of the long-haired dogs, in only 3.9% of the short-haired dogs, and accounts for approx. 30% of genotypes found in medium-haired dogs. Three breeds with very long hair –the Silky Terrier, the Yorkshire Terrier and the Afghan Hound– are an exception. These breeds do not differ from the short-haired breeds as far and the FGF5 gene is concerned, suggesting that additional genes exist that contribute to hair length in dogs.
For this gene, or L (for “length”) locus, the two alleles that determine hair length are, in dominance hierarchy:

L = short hair
l = long hair

Which opens up to a collection of three possibilities:

homozygous LL = short hair
heterozygous Ll = short hair that carries the long hair allele
homozygous ll = long hair

By way of reminder, in most breeds, the dog's hair grows to a given length, then growth ceases. In some breeds, hair growth doesn't cease, and the dogs don't shed. The Poodle and the Bichon Frise are among the best known.

2. The gene for “facial furnishings”

The RSPO2 gene, located on chromosome 13, controls the presence, or absence, of “facial furnishings”. These “furnishings” are only found in combination with the “wire hair” trait. Research confirms that the presence of these “furnishings” results from a dominant allele. It means that a single allele is sufficient for the development of “furnishings”. Thus, this allele is not found in “unfurnished” dogs.
For this gene, or Wh (for wire hair) locus the two alleles are, in dominance hierarchy:

Whw = wire hair
wh = smooth coat

Which opens up to a collection of three possibilities:

homozygous WhwWhw = wire hair with “furnishings”
heterozygous Whwwh = wire hair with “furnishings” that carries the wh allele
homozygous whwh = smooth coat

The dominant Whw allele is epistatic (rare cases of incomplete dominance exist) to the L locus. The recessive wh allele favours expression of the alleles at the L locus.

3. The gene for “curls”

The KRT7 gene, located on chromosome 27, controls the presence, or absence, of “curls”. Research has shown that the gene is always associated with either the pair of “ll” (long hair) alleles, or with the “Whw” allele, or even with both.
For this gene, or Cu (for “Curly”) locus, the dominant or recessive characters feature more complexities. Burns & Fraser (1966) concluded that the curly coat trait dominated over the straight coat trait. In the book “The genetics of the Dog” (2nd edition – CAB International 2012) by Professeur G.S. Barsh, an overview chart also refers to the curly hair trait as being dominant. The heterozygous gene curly coat/straight coat would produce a kinky, or wavy, coat.
It should be mentioned that, in the Belgian Shepherd Dog breed, curly coats and wavy coats are considered a fault.

Summary

The combination of these three genes magnifies their effects; together, they account for the seven coat types found in most purebred dogs. The Belgian Shepherd Dog breed features three of the seven types: the short hair, the long hair and the wire hair traits, as calculated from the genetic formulae shown in the table below:

Phenotype Length Furnishings
Short hair LL or Ll whwh
Long hair ll whwh
Wire hair LL or Ll WhwWhw ou Whwwh

For your reference, the other four phenotypes in these combinations are listed hereunder:

Phenotype Example
Curly with “furnishings” Airedale Terrier
Long with “furnishings” Bearded Collie
Long and curly Irish Water Spaniel
Long, curly with “furnishings” Bichon Frise

Aside from the three key genes (L, Wh and Cu), two other genes have come to be known: the Hr (Hairless) gene for hairless dogs and the R (Ridge) gene for the ridge on the back of the Rhodesian Ridgeback breed. The ridge is formed by the hair growing in the opposite direction to the rest of the coat.

To conclude, the study significantly advances scientific knowledge in the field of dog coat texture. There can be no doubt that more focussed research will soon complement and refine our knowledge further.

Jean-Marie Vanbutsele