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Coat colours in dogs
What are 'coat colours'?
DNA tests for coat colours
Breeds that can be tested
The DNA tests for the genotypes of the E-locus and the B-locus can help
the breeder to be in control of the major coat colours of the pups born in the next
generation. The tests give him a choice to avoid pups with certain coat colours in his
litters or, if he likes, to produce pups of those colours willingly.
E-locus (yellow versus black or brown)
Every dog that shows black or brown eumelanin in its coat has at least one allele E.
So it must have either the homozygous genotype EE or the heterozygous genotype Ee.
For the breeder it can be important to know the genotype of his breeding animals: from
combinations where both parents carry the allele e yellow pups (ee) will be born.
| Mating combinations for the E-locus |
|
Parents
|
Offspring |
| EE x EE |
100% EE |
|
|
| EE x Ee |
50% EE |
50% Ee |
|
| EE x ee |
|
100% Ee |
|
| Ee x Ee |
25% EE |
50% Ee |
25% ee |
| Ee x ee |
|
50% Ee |
50% ee |
| ee x ee |
|
|
100% ee |
The DNA test for the E-locus can be applied in every non-yellow breed or,
more correctly: in every non-yellow animal. Especially in breeds where the breed
standard excludes yellow pups applying the test can avoid disappointments in a next litter.
On the other hand, in breeds where yellow is an appreciated colour, testing for the genotype
of the E-locus can help the breeder to choose the right sire for his bitches to
produce yellow offspring. It is all a matter of applying the right parental combination
after the genotypes of potential parents are known.
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B-locus (black versus brown)
Every dog that shows black eumelanin in its coat has at least one allele B.
So it must have either the homozygous genotype BB or the heterozygous genotype Bb.
For the breeder it can be important to know the genotype of his breeding animal:
from combinations where both parents carry the allele b brown (chocolate, liver) pups (bb)
will be born.
| Mating combinations for the B-locus |
|
Parents
|
Offspring |
| BB x BB |
100% BB |
|
|
| BB x Bb |
50% BB |
50% Bb |
|
| BB x bb |
|
100% Bb |
|
| Bb x Bb |
25% BB |
50% Bb |
25% bb |
| Bb x bb |
|
50% Bb |
50% bb |
| bb x bb |
|
|
100% bb |
In general the DNA test for the B-locus can be applied
in every breed with black eumelanin or, more correctly: in
every animal with black eumelanin. Especially in breeds where the breed
standard excludes pups with a brown coat or with brown noses and eyelids
applying the test can avoid disappointments in a next litter. On the other hand,
in breeds where brown (chocolate, liver) is an appreciated colour, testing for the
genotype of the B-locus can help the breeder to choose the right sire for his
bitches to produce brown offspring.
For the time being there is one important limitation in applying the DNA test for the B-locus.
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There is not just one allele for brown (not just one b-allele), there are at the
moment three known alleles and in the near future probably a few more will be found. So
before the test can be applied for a breed, we have to make sure that the brown colour in
that breed is caused by one of the alleles that can be detected. The B-locus DNA test
has to validated for every next breed.
At this moment the DNA test for the B-locus is fully validated for the breeds
Labrador Retriever, Flatcoated Retriever and Dalmatian. For other breeds
we have to check to make sure that the brown colour does not result from the action of an
allele that is not yet included in the DNA test.
E-locus and B-locus (yellow dogs with brown noses and eyelids)
The allele e for the absence of eumelanin only affects the eumelanin of the coat,
not in the skin. So ee-animals will have a coat colour that can vary between
mahogany red and pale yellow but will have eumelanin pigmented noses and eyelids.
In many breeds the combination of a yellow coat with a brown nose with brown eyelids is
not accepted. In some cases because the standard excludes such animals, in other cases
because the breeders do not like that combination of coat and skin colours.
In Dalmatians the coloured spots normally are black or brown
(liver) as a result of the eumelanin in the coat. Every now and then 'lemon'
animals are born. Lemons are animals that do not have eumelanin in their coat (ee).
The colour of their spots varies between pale yellow and bright orange and the nose and
the eyelids are eumelanin pigmented. If we have a lemon animal with a brown (liver) nose
and brown (liver) eyelids (bb), we call it 'orange'.
We can list the minimum requirement for the E-locus and B-locus genotypes
for the four coat (and skin) colours in Dalmatians using a 'dot' for alleles that
are not relevant for the phenotype:
| Phenotype |
Genotype |
|
| Black |
E. B. |
Any black spotted dog could carry the alleles e and/or b |
| Brown (liver) |
E. bb |
Any brown (liver) spotted dog could carry the allele e |
| Lemon |
ee B. |
Any lemon spotted dog could carry the allele b |
| Orange |
ee bb |
Orange spotted dogs show their genotype for colour phenotypically |
The genotypes of breeding animals can be established with the DNA tests for the E-locus
and the B-locus which makes it possible to avoid pups of unwanted colours to be born.
If we exclude all lemon and orange animals from our breeding programme,
-
lemon pups are born only from two parents carrying the allele e (so from Ee x Ee),
-
orange pups are born only from two parents that both carry the alleles e and b (so from EeBb x EeBb).
If a Dalmatian had excellent qualities in every respect and its only failure
would be that its colour is lemon (eeB.) or orange (eebb), the DNA tests
could help us to preserve its good (maybe even valuable) genes for the gene pool. If we
can find a mating partner that is proven to be free from the allele e all offspring would
have eumelanin pigmented spots in their coat and would be either black spotted (EeB.) or
liver spotted (Eebb).
.jpg)
Breeders of Labrador Retrievers can have a comparable 'colour problem'. Yellow
(ee) is an accepted colour and yellow dogs should have a black nose and black pigmented
eyelids (they should be eeB.). Since brown (liver, chocolate) is an accepted
colour as well it can hardly be avoided that incidentally 'yellow livers' (eebb)
are born. These animals have a brown nose and brown eyelids and therefore loose some of the
expression of there face that is typical for the (normal) yellow black (eeB.).
Breeders can avoid yellow liver pups to be born. They can apply the DNA test for the
alleles of the B-locus for their yellow breeding animals and the DNA tests for the
alleles of the B-locus and the E-locus for their black and brown
(liver) animals. The information on the genotype of their breeding animals gives them the
opportunity to find the right mating partners for their dogs.
If a Labrador Retriever had excellent qualities in every respect and its only
failure would be that its colour is yellow liver (eebb), the DNA tests could help us
to preserve its good (maybe even valuable) genes for the gene pool. If we can find a mating
partner that is proven to be free from the allele e all offspring would have an
eumelanin pigmented coat and would be either black (EeB.) or liver (Eebb). If we
can find a mating partner that is proven to be free from the allele b all offspring
would have black eumelanin in their noses and eyelids.
In any other breed where brown (b) or yellow (e) are of importance in the
selection programme the DNA tests for the B-locus and/or the E-locus can help the
breeder to make the best decisions.
The brown colour of eumelanin is quite often less favoured, not only in the noses and
eyelids of yellow dogs of some breeds, also in dark masks, brindle patterns or saddle
patterns of other breeds. The same holds for the lack of eumelanin, in many breeds yellow
dogs are not accepted but will be born from time to time as long as the allele e exists
in the population.
Breeding policy
Testing for coat colours
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