Brown
(B Locus Gene)
 

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!

 
photos   Brown Great Dane aka Kiss My Cocoa
 

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.


photo   Brown Great Dane aka Kiss My Cocoa
 

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.

 

 

The Dilute Chocolate


photos   Brown Great Dane aka Kiss My Cocoa
 

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.

 

This from Healthgene:
Great Danes occur in a wide variety of coat colors. Although the alleles causing all the coat colors have not yet been identified, DNA tests are available to identify the presence of some of these, which are outlined below.
There are two common alleles in Great Danes at the
E locus: Em and E. Em produces a melanistic (dark) mask. It is only visible on fawn or brindle dogs. So the mask is not visible on Harlequin, Mantle, merle, or white Danes, and is not distinguishable from the body color on black and blue Danes. Since the presence of mask is dominant to its absence, one does not know if a dog with a mask is Em/E or Em/Em, unless one parent did not have mask without DNA testing.

Blue in Great Danes is caused by the presence of two
d alleles. Blue is carried by some black, fawn and other colored Great Danes. A dog with only one d allele is never blue, but can produce blue. A d/d genotype would cause a fawn Great Dane to have a blue mask instead of a black mask if the Em allele is present. A d/d genotype would cause a brindle Great Dane to have blue instead of black stripes on a pale fawn.

All Great Danes are
ay/ay at the agouti locus so there is no need to test for alleles at the agouti locus. Although DNA tests are not yet available for alleles of the K locus, recent research has shown that black or blue dogs have at least one K allele. At the present time there is no test to distinguish which black or blue dog might carry brindle or fawn, which is caused by the presence of recessive alleles at the K locus.
Brindle dogs have at least one copy of the
kbr allele (they may have two).  Fawn dogs do not carry brindle because they are k/k. There is also no DNA test for Harlequin at this time. It has recently been proven that Harlequin dogs all carry at least one copy of the merle allele.

Notes
Danes can carry one of the alleles causing brown, although these are very rare. Dogs that are
b/b, will have chocolate coats instead of black or pale brown coats instead of blue. The markings would be chocolate on the Harlequin or merle dogs. Testing for the b alleles is not routine, but is available at no extra charge.

The alleles at the
A and E locus were identified by a collaborative research project between the labs of Dr. Greg Barsh at Stanford University and Dr. Sheila Schmutz at the University of Sascatchewan, who also identified the B locus alleles. The d allele has been identified by a collaborative research project between the labs of Dr. Tosso Leeb and Dr. Schmutz. Many dogs owners helped by contributing either individual samples or samples from complete litters.


 

 


  Brown Great Dane aka Kiss My Cocoa