Dog coat colour
Dog coat colours developed through natural and human selection. Protective colours that allowed better survival in nature were favoured by natural selection. When dog was domesticated, intense human selection had a major role in the development of new coat colours. In most dog breeds, breeders prefer certain coat colours to the others and some are even forbidden by breeding standards. Knowledge about the genetic code involved in coat colour determination is of key importance to the breeder who wants to breed puppies of certain colours.
At the moment tests for six key loci, which determine coat colours in dogs, are available. There are some additional loci that are involved in coat coloration, but there are no tests available. Genetic tests provide information about genotypes on certain loci and identify recessive alleles, which are not expressed in coat colour. Each locus has two alleles, one inherited from mother and one from father. If both alleles are identical, the animal is homozygous. If two different alleles are present, the animal is heterozygous and expresses dominant allele. Information about genotypes on certain loci enables breeders to mate their dogs with expected results (coat colour).
More information about the function of each individual locus can be found in the description of the test.
- E locus (yellow-red vs. black)
- EM locus (melanistic mask)
- B locus (chocolate or liver brown)
- K locus (determines whether A locus is expressed)
- A locus (agouti, affecting pigment distribution)
- D locus (dilution, affecting pigment intensity)
Coat pigmentation in dogs
There are two types of pigment, which determine coat colour in dogs and most other mammals: black eumelanin and yellow-red pheomelanin. The synthesis of these two pigments in melanocytes is regulated by melanocortin system in which a key role is played by agouti protein (ASIP) and melanocortin 1 receptor (MCR1R). In dogs β-defensin 103 protein (CBD103) is also important in coat coloration.
Each pigment (eumelanin, pheomelanin) has its own colour, which is regulated by the action of different genes. Genes coding for coat colour in dogs determine colour shades and colour distribution (can be random to the certain degree). Sometimes genes do not allow production of pigments which results in white coloration. Switch in pigment production during hair growth results in striped coloration, which results in agouti coat colour.
Chart: dog coat colour loci.