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Coat colours in dogs
What are 'coat colours'?
DNA tests for coat colours
The absence of eumelanin in the coat is inherited as an autosomal recessive trait,
the allele for it is located on the E-locus. The allele for the absence of eumelanin
(e) is found in almost all breeds that (should) have a coat colour with eumelanin
pigment (E). Eumelanin in the coat is a preferred or even required characteristic
in some breeds and animals with the ee-genotype in those breeds are excluded from
the breeding programme; breeding animals should have the EE- or Ee-genotype.
In other breeds it is the other way around, eumelanin in the coat is not accepted according
to their breed standard; all animals of those breeds will have the ee-genotype.
The E-locus DNA test yields three possible outcomes:
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Your dog is EE (it has two alleles for the normal production of eumelanin).
In its coat it will show (black or brown) eumelanin and, in some breeds just as
important, it will not pass on the allele for 'absence of eumelanin' (e) to
the next generation.
-
Your dog is Ee (it has one allele for the normal production of eumelanin
and another one allele for the absence of eumelanin). It will show (black or brown)
eumelanin in its coat but it will pass on the allele for 'absence of eumelanin' (e)
to half of its offspring.
-
Your dog is ee (it has two alleles for the absence of eumelanin). In its
coat it will show no (black or brown) eumelanin and it will pass on the allele
for absence of eumelanin (e) to all of its offspring in the next generation.
So the dog's coat colour must be of a colour shade between mahogany red and pale yellow.
It is important to remember that the ee-genotype does not affect the eumelanin of nose
and eyes.
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The brown colour of eumelanin is also inherited as an autosomal recessive
trait, the allele for it is located on the B-locus. In almost all breeds
that (should) have a coat colour with black eumelanin (B) the allele for
brown eumelanin (b) is found. In some breeds a black coat is a preferred
or even required and animals with the bb-genotype in those breeds are excluded
from the breeding programme; breeding animals should have a BB- or
Bb-genotype. In other breeds it is the other way around, black eumelanin
in the coat is not accepted according to their breed standard; all animals of
those breeds will have the bb-genotype.
The B-locus DNA test yields three possible outcomes:
-
Your dog is BB (it has two alleles for the production of black eumelanin).
In its coat and in the pigmented parts of the skin it will show black eumelanin
and, in some breeds just as important, it will not pass on the allele for brown
eumelanin (b) to the next generation.
-
Your dog is Bb (it has one allele for black eumelanin and another one allele
for brown eumelanin). In its coat and the pigmented parts of the skin it will show black
eumelanin but it will pass on the allele for brown eumelanin (b) to half of its offspring.
-
Your dog is bb (it has two alleles for brown eumelanin). In its coat and the
pigmented parts of the skin it will show brown eumelanin and it will pass on the allele
for brown eumelanin (b) to all of its offspring in the next generation.
A problem in the DNA test to detect b-alleles in animals that are phenotypically
black (BB or Bb) is that there is not just one allele for brown
eumelanin (not just one 'b'). Apparently in time there have been several
mutations on the B-locus of the dog with at each occasion a different change
in the structure of the DNA of the gene (for Tyrosinase Related Protein 1). Although
the mutations resulted in different alleles at DNA level, they all resulted at the
level of the eumelanin synthesis in one and the same 'disorder' causing the phenotypic
expression of eumelanin to change from 'black' to 'brown'.
At this moment we know of at least three different b-alleles but surely there
are more to be found. So before we can apply the B-locus DNA test for a breed
it has to be validated, we have to make sure that the b-alleles in the test are
the ones that cause the brown eumelanin for that breed.
Breeds that can be tested
Breeding policy
Testing for coat colours
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