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The control of coat
and pattern in mammals is complex. In dogs, several
genes have been associated with coat colour including:
A (agouti), B (brown), C (albino), D (blue dilution),
E (extension), G (greying), M (merle), R (roaning),
S (white spotting) and T (ticking). HealthGene Laboratory
offers DNA tests for B and E color genes to determine
the following colors in canines: black, brown or red.
The gene responsible for red or black coat color is
called the Melanocortin Receptor 1 gene (MC1R). This
gene has two common forms (alleles) represented as E
and e. When E (dominant allele) is present in a dog,
it has some black or brown in its coat. Dogs that posses
two mutated forms of the gene, represented as ee (recessive),
are red or yellow in color depending on the breed.
The gene responsible for brown color in dogs is known
as Tyrosinase Related Protein 1 (TYRP1). The normal
(B) form of this gene is dominant to the mutated (b)
form. The TYRP1 gene is also affects the nose leather
and pads. For example, in dogs that are yellow or red
(genotype ee), TYRP1 mutations (bb) change the nose
and pad colouration from black to brown.
Terminology for coat colors used by various dog breeders
and associations varies considerably. Liver, chocolate
and brown are all names used to describe various shades
of deep brown. Orange, red, yellow, gold and apricot
are all used for shades produced by the mutated MC1r
gene. Occasionally, some owners use the term liver instead
of orange. Another confusing example is the use of red
for brown in the Australian Shepherd. Clearly, understanding
the inheritance of coat color in some breeds has been
complicated by the use of some terms which may not correlate
with the different forms of the MC1R and TYRP1 genes.
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Until recently, no
definitive method for predicting a dog’s coat
and nose color was available. Canine breeders could
only guess the future color of puppies based on the
coat and nose colors of the breeding parents. At best,
this method provided breeders with an estimate as to
the likelihood that a puppy would be a certain color.
However, under specific circumstances (i.e. the sire
and dame are of EeBb genotype), this method is of no
value since two dogs (ex. Labrador Retriever) of the
same coat and nose color (black) could potentially
produce puppies of various colors (black, chocolate,
yellow). This suggests that knowing a dog’s coat
and nose color is of little use with regards to predicting
a puppies future colors unless the hidden genetic color
of the dog is also known.
Recently, advances in DNA technology have led to the
discovery of two genes associated with canine coat and
nose color. This discovery has led to a DNA-based test
that enables breeders to determine the hidden colors
of their dogs, and successfully predict the future coat
and nose colors of their pups. This information can
be crucial to satisfy breed standards for dog registration.
Using this test, breeders can selectively choose breeding
partners that are most likely to produce offspring with
the desired coat and nose color.
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