Diluted or Pale Colors
This webpage is part of a series on Dog Coat Color Genetics and was last updated on October 3, 2009 by Sheila Schmutz
Dilution of Eumelanin and/or Phaeomelanin
Blue or charcoal grey, as a dilution of black, has recently been shown to be caused by the melanophilin gene (MLPH). The blue caused by this gene could be termed "born blue" since it is present from birth. The Blue Doberman is a dog that has the black on its upper torso diluted to slate grey and its tan undersides diluted to a paler shade of tan. The dilution of the tan is much less noticeable than the dilution of black, both both eumelanin and phaeomelanin are affected in dogs of "d/d" genotype.
Blue is the name of a coat color used in breeds like the Great Dane to specify a eumelanin pigmented dog that is diluted to a blue grey. The litter at the left shows blue and black pups in the same litter.
Blue is also used to describe a coat color in the Chow, as shown by Shadow on the right, and in the Shar-Pei. It also occurs occasionally in Newfoundlands, Large Munsterlanders, Australian Shepherds, Doberman Pinschers, and other breeds. Hence it occurs in a wide variety of breeds and may be quite ancient in origin.
The Weimaraner is an example of a brown dog with a diluted coat color. This dog is most commonly seen as the short-haired variety on the right, but there is also a long-haired variety shown below. Although Little refered to the Weimaraner as diluted brown, most people call this dog the "grey ghost". Most Weimaraners are b/b at the brown locus and therefore Little was right again! He also referred to them as "d/d" at the dilute locus. Some slate grey dogs resulted from breeding a Weimaraner colored dog to a black dog occur, suggesting this diluter gene is capable of diluting both brown to the Weimaraner pale brown color and black to a slate grey. Little called this color blue in a Great Dane/Pointer crossbred pup.
The photo at the right shows that MLPH is able to dilute both black and brown eumelanin pigments in these Labrador Retriever pups..
|Photo by Linda Heeg|
In dogs such as the Australian Shepherd, dilution causes black-and-tan dogs to appear charcoal-and-tan. The tan is not affected as dramatically as the charcoal. Kodak is charcoal-and-tan and Peggy is blue merle with tan. The merle seems to make her tan seem even paler than his tan! Notice the marked difference in their nose color however. His is charcoal compared to her pitch black. (Photo by Jonelle Kunkle)
Italian Greyhounds occur in "blue" and also "blue fawn". Nelson is a good example of a dog that has his black mask diluted to grey and his fawn body diluted to a paler fawn. The Italian Greyhound Club of America is providing funding to study IGs that have dilute coat colors with and without hair loss or skin problems. We have already determined that not all dilute IGs have the same MLPH mutation.
Some blue dogs appear to be more prone to skin problems and hair loss, and perhaps skin allergies than dogs that are black. Some breeds have more problems in "born blue" dogs than others. The current phase of our study is to try to understand this difference.
The hair loss and skin problems which occurs in blue dogs is called "Black Hair Follicular Dysplasia" in some breeds and "Color Dilution Alopeicia" in other breeds. In the past it may sometimes have been called "Blue Dog Syndrome" also.
DNA Tests for "d" Allele
HealthGene offers tests for the common "d" allele. In some breeds such as Large Munsterlanders, Newfoundlands, and Great Danes, this appears to be the only allele causing grey/blue. In other breeds such as Doberman Pinschers, Italian Greyhounds, Chow Chows and Shar-Pei the test could detect carriers of this allele also, but this is not the only allele that causes grey/blue.
In other breeds, such as the English Setter, a blue belton means the dog is black and white giving a bluish appearance from a distance. In the case of the "blue belton", no dilution is involved. That phenotype is an affect of the roan, ticking and/or spotting series. Blue in the Blue Heeler is likely a description for roan. (See spotting page for other examples.) Blue merle is the term used for merle dogs with black and grey and white hairs in the marbled or merle pattern as illustrated by Peggy, the "Aussie" above. (See merle page for further information.)
Other Dilution Genes
In several other species, more than one dilution gene has been identified. One of these is thought to be Tyrosinase Related Protein 2 (TRYP2). In mice, this gene dilutes black coat color to slaty grey and another name for the gene is therefore "slaty". Yet another name, based on it chemical composition, is DCT or Dopachrome tautomerase. This gene has been mapped to dog chromosome 22. In mice this DCT gene acts as a co-dominant I am unaware of a breed of dogs that has black, charcoal and pale grey so this gene may have no variants affecting coat color in dogs.
Some poodle fanciers are concerned that the black in their breed is not as black as in breeds like the Labrador Retriever. I believe that may simply a side effect of the hair type that is characteristic of Poodles. However Poodles do have both the alleles for dilution and progressive graying and therefore many Poodles who might be black are blue or silver instead.
A black poodle, Shadow, owned by Mrs. Ventner has become famous because it was the dog whose DNA was used by Celera to obtain the first "complete" dog sequence. IF there is something unique about poodle black.......Shadow would reveal that eventually. Shadow is 7 years old in the photo from Science magazine, September 26, 2003 issue.
A larger effort to get a more detailed dog DNA sequence is now well underway at NIH. A Boxer has been used for the main dog in that study but about 9 other dogs of different breeds and a wolf will also be partially sequenced. Much of this sequence is already available through GenBank.
In many species, such as cats, rabbits, mice and cattle, there is a mutation that causes a temperature sensitive loss of pigmentation in the warm parts of the body. The dog at the left looks like the dog equivalent of a chocolate point Siamese cat. He was apparently found as a pup on the streets of Russia, but then disappeared again. It would have been interesting to study its tyrosinase sequence.
To date no mutations affecting dog coat colors have been found in the coding sequence of Tyrosinase, the typical gene associated with the C locus in most other species.
Little discusses another hypothetical C allele, (cch). He uses this allele to explain both a pale brown and a pale red, which would imply it could dilute both eumelanin and phaeomelanin. He further states that phaeomelanin will be diluted before and more than eumelanin. In most species, both eumelanin and phaeomelanin are affected if TYR is mutated. However, MATP (now called SLC45A) in horses has been shown to be a gene that affects the dilution of phaeomelanin and eumelanin differently by researchers in Davis, CA and in France. MATP mutations cause the "palomino/bucksin" colors in the horse. We have recently shown that this gene does not seem to cause dilutions to cream in several breeds of dogs.
Whether this poodle's pale coat color is caused by cch or some other gene has not been proven. We do know that pale poodles or any other cream dog that we've studied does not have a mutation in the tyrosinase gene though, so the chinchilla name is not that appropriate.
Sponenberg and Rothschild (2002) state that the cch allele affects ONLY phaeomelanin but this is not likely because the mouse mutant found in 1922 for which the chinchilla allele is best known, dilutes both melanin pigments.
The photo above dramatically illustrates the effect of a co-dominant phaeomelanin diluter gene. The hair clippings are from Toy poodle ears: red, apricot, and cream. Their dam was a black that was not diluted to silver, although she was not pitch black either. She must carry some dilution allele to have a cream pup.
Sponenberg and Rothschild describe a gene they name I for Intense that dilutes only phaeomelanin. Diluted phaeomelanin colors are sometimes called cream, buff, apricot, lemon, etc. Such a gene, undoubtedly exists. However this gene has not yet been identified or even mapped in the dog.
Kaschmir, the Afghan Hound on the right, is a striking example of a dog that only dilutes phaeomelanin and not eumelanin. His mask is still very black, even though his body is almost white. For specific information on color testing in Afghans, please see their separate page.
|Photo by Barbara Lessmeister|
Another example of dilution of phaeomelanin only occurs in Tervuren. Buzz on the left demonstrates undilted red hairs, wheras Kosh has diluted red hairs. Both retain undiluted black hairs in their masks and intermingled on their bodies. Kosh would be called a grey by many Tervuren owners, quite understandably, but this further adds to the confusion around the term grey.
Some authors refer to brown as a dilute color. Somehow this bothers me. I don't think of brown as diluted black, which to me is gray or in dog terms "blue". Brown is created by a modification of eumelanin, so in some sense I suppose I can understand why it is sometimes lumped with the diluter gene effects.
The gene for brown is TYRP1 and the 3 mutations causing brown are now known but this is discussed on another page about brown in this series.
|Locus Symbol||Gene||Action||Proven in Species||Dog Chromosome|
|D for dilute (Little)||MLPH||eumelanin diluted to grey or blue & phaeomelanin paled||mouse, dog||25|
|C for color (Little)||tyrosinase (TYR)||albinism, dilutes phaeomelanin & eumelanin||mouse, cattle, human||21|
|P for pink-eyed (Little)||P gene||pink eyes & "white" coat||mouse||5|
|G for greying (Little)||???||progressive greying||poodles and horse||?|
|I for Intense (Sponenberg)||???||only phaeomelanin diluted||?||-|
|?||MATP||phaeomelanin diluted as co-dominant, eumelanin as recessive||horse (palamino & buckskin, cremello & perlino)||4|
|Slaty||TYRP2||eumelanin co-dominant dilution||mouse||22|