This coloration is often referred to as
"Red." Genetically, this color is brown and is the
homozygous recessive allelic pair, "b/b."
The brown locus
(the
position of a gene on a chromosome. Every gene has a specific
locus)
affects only eumelanin (affects only black/brown, not
red/yellow.) It is believed that the brown locus codes
for an enzyme, tyrosinase-related protein 1 (TYRP1), which
catalyzes the final step in eumelanin production, changing the
final intermediate brown pigment (dihydroxyindole) to black
pigment. So, ALL dogs start
as BROWN and after the final
step... this directs the color to be black!
The chocolate gene is found in quite a few
breeds; e.g., the liver Dalmatian, chocolate Poodle, chocolate
Dachshund, the Vizsla and the
liver Shorthair, to name a few. All these breeds carry the
genes, although the resulting shades of red or liver vary with
the different breeds. This same
gene causes brown in several other species, such as mice,
cattle and cats. Brown is a type of eumelanin pigment.
When brown (b/b) is
expressed, it means that the final step in eumelanin
production has not been completed and the pigment remains
brown. The brown color is NOT a genetic defect.
When the
alleles are in the homozygous or heterozygous dominant form of
B/B or B/b, the color and pigment (nose, eye rims and lips)
remains (detects the color to be) black.
When the
alleles are in the homozygous recessive form (b/b), the color
and pigment will be brown. This just means that the
final step in eumelanin production of changing brown to black
did not occur. Phaemelanin (yellow/red/{e/e}) is not
affected. However, in the e/e colored dog, if the dog is
also b/b, they will be either red or yellow and will have
brown pigment (nose, eye rims and lips {as shown with the chocolate fawn
below}.)
The pigment granules produced by "bb" are smaller, rounder in
shape and appear lighter than pigment granules in "B" dogs.
The iris of the eye is also lightened to amber, gold, olive
greenish-gold or an orange coloration.
In order to produce the
brown color both parents could be the brown/chocolate color
(b/b) or one of the parents must be the brown/chocolate color
(b/b) with the other parent carrying the brown/chocolate
allele (B/b) or both parents (which could be any color in
"appearance") must be a carrier of the "B" gene in the
heterozygous form (B/b) aka recessive chocolate.
So, the rule of thumb is if
two brown dogs are mated, the resulting offspring can not be
black nor can they be blue.
If two brown dogs are mated
and neither are carrying the dilution gene then the offspring
will be all brown/chocolate.
If two brown dogs are mated
and one is carrying the dilution gene and the other is not,
then the offspring will be all brown/chocolate.
If two brown dogs are mated
and both are carrying the dilution gene, then the offspring
could be either brown or diluted brown.
Now, if you see a black
puppy in a litter where both parents are brown/chocolate, lol,
then that puppy has a different sire because it is genetically
impossible for two brown (b/b) dogs to produce black (B/B or
B/b) offspring.
The DILUTE chocolate/brown
(above) in the Dane breed is called Lilac. This color is often
times mistaken to be blue or even cream. When in doubt
look at the NOSE color. The dilute will have a
rosy-brown with a slight grayish tint colored nose. The
blue will have a gray to dark gray (almost black) nose.
The lilac color is a result of
the brown (b/b) pigment being affected by a dilution (d/d)
gene. The dilution gene is found on the "D" Locus.
When the "D" allele is in the homozygous form "d/d," it
dilutes eumelanin (black) pigment to a grayish or bluish
color. It also lightens and dulls phaeomelanin (reds and
yellows) to a flat or silvery shade of yellow to red color.
Skin pigment will also be a
lighter color and the iris may be a lighter brown, amber, gold
or gray.
The coloration is achieved by
breeding together dogs that carry the dilution gene either in
it's homozygous or heterozygous form; (D/d or d/d) and the
chocolate gene (B/b or b/b) either in it's homozygous or
heterozygous form. The resulting offspring's genotype
for lilac would be (b/b d/d) (brown + dilution).
Black to black, or black to
chocolate, or chocolate to chocolate, or a black to blue, or
blue to chocolate can produce lilac colored offspring IF the
genes pair correctly and IF they are BOTH carrying the
recessive form of the "B" and "D" gene (which is "b" and "d"
respectively).
The lilac color is the result
of two recessive genes, therefore, the pup could be affected
with Color Dilution Alopecia (a skin condition). Not all
are but many do have some form of a skin/coat condition.
