Canine Coat Color Testing
MAKING SENSE OF CANINE COAT COLOR TEST: A GENETIC APPROACH
This article is intended to help you in understanding the genetics of canine coat color. Even though not all aspects can be covered in one article, we will focus on genes that are now available for testing.
The pigment that is responsible for a dog’s hair color is called melanin. There are two types of melanin in dogs: a pigment associated with black and brown coloration (called eumelanin) and a pigment associated with lighter colors such as yellow, red and orange (called phaeomelanin). There are a number of genes that affect how and where these pigments are produced. The genes can occur as variant forms, called alleles. Some alleles play a dominant role (usually identified by capital letters) over others and their presence will overshadow the effect of recessive alleles (identified by small letters).
The gene designated as E is responsible for eumelanin production. If the dominant form of E is not present (ee genotype), the black and brown pigment is not produced and the dog’s coat will be reddish in color (yellow, orange or red). On the other hand, if at least one E allele (EE or Ee genotypes) occurs, black or brown pigment would be the basis for a dog’s coat color. A third allele, EM, causes reddish dogs to have a black or brown facial mask (Briards, Italian Grehounds). An EG allele is necessary for Afghan Hounds to show the pattern known as “domino” and for Salukis to show the pattern known as “grizzle”. The dominance hierarchy is EM > EG > E > e at this locus.
The absence of the dominant form of B will change the black color of eumelanin into brown but will have no effect on the coat color of ee genotype dogs. For example, dogs with EEBB, EeBB, EeBb genotypes will have eumelanin normally produced (E is present) and will have black coat color (the dominant B is present). EEbb and Eebb genotypes will have eumelanin produced but their coat will be brown in color (B is not present). Note that any bb genotype dog will have brown nose and pad leather. The eeBB, eeBb, and eebb genotype dogs do not produce eumelanin pigment and will have reddish coat color.
The A gene is a bit more complicated. This gene controls where and how two pigments are produced on the body or even on the individual hair. It is very important to understand that the effects of this gene depend on the ability to produce eumelanin, which does not occur in ee genotype dogs. The most dominant allele in this group is thought to be aY, which causes sable and fawn coloration of the coat. Sometimes the reddish hair has black tips. Some examples of this type of dog are sable Collies and Shetland Sheepdogs as well as fawn Great Danes and Pugs. The next allele in dominance is aW, which is characterized by alternately banded hair and sometimes is called “wild type”. This type causes hair to change its color during growth from light to dark resulting in bands as seen, for example, in some German Shepherds or wolves.
The black-and-tan allele, at, gives a black dog its tan markings. This is typical of many hounds (Afghan Hound, Dachshund, Saluki) as well as Rottweilers and Doberman Pinschers. The same allele is responsible for tri-color dogs (black-and-tan with white), for example in Shetland Sheepdogs. The last allele is a recessive black “a”, which is considered to be recessive to all other allele in the A group. Such aa genotype dogs are black. This can be seen in German Shepherds and Shetland Sheepdogs (bi-color).
There are other groups of genes responsible for coat coloration. They are C (albino), D (blue dilution), G (graying), M (merle), R (roaming), S (white spotting), T (ticking), and K (dominant black). The work of identifying them is still in progress. HeathGene Laboratory would like to thank Dr. Sheila Schmutz from the University of Saskatchewan (Canada) for her dedication and support in this research.