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Brindle in Dogs: New Information about Stripes

We all thought we had brindle in dogs pretty much figured out. We all knew that brindle was recessive to dominant black and dominant to wild-type (KB>Kbr>ky). Recent research however, has thrown that idea on it’s head. Researchers in Europe have discovered that, at least in some breeds, brindle dogs test positive for the dominant black allele. That’s right, some brindles test positive for dominant black. Wait you ask...Wouldn't that make them black? Well it turns out, no, it doesn't. In fact, all the brindle dogs tested (14 brindle Boxers and and 10 brindle Great Danes), tested heterozygous for the dominant black allele and wild-type (KBky) .

A Brindle Boston Terrier

A Brindle Boston Terrier

These researchers didn't intend to throw our understanding of brindle on it’s head. Their intention was to study agouti and it’s interaction with brindle but because the mutation(s) that cause brindle have not been located, they tested all the dogs in the study for dominant black and the wild type at the K locus (KB and ky). They were very much surprised when all the brindle dogs in the study came back as carrying one copy of dominant black and one copy of wild-type (KBky). This might seem surprising at first, but this isn’t the first time that a brindle dog has tested positive for dominant black. A group of Japanese researchers studying Akita-inu dogs also found that their brindle dogs tested positive for one copy of dominant black (there were no homozygous dogs found in the study). Even more interesting, black isn't even an recognized color in Japanese Akita-inu’s. This means that the dominant black mutation itself seems to be, at least partly, responsible for brindle. And we are talking about the exact same mutation (CBD103 G23del) that has been found to be responsible for dominant black in other breeds. It is also unlikely that an addition mutation at extension or agouti is affecting expression of dominant black vs brindle because these dogs carried mutations at extension and agouti for which we can test. In the Japanese study, all the Akita-inu dogs studied tested positive for the fawn allele at agouti (ay), even the brindle ones and in the European study all the dogs tested positive for black mask (Em).

So what does this mean? Well, that remains to be determined. It may mean that brindle is not at the K locus at all but is a yet to be discovered modifier of dominant black (KB). It’s possible that Akita-inu’s are homozygous for this yet to be determined mutation so that all Akita-inu’s that are positive for the CBD103 G23del mutation (dominant black) are brindle rather than dominant black. It could also mean that their are different types of brindle among dogs with some breeds having a brindle allele at the K locus and some breeds having a modifier at another locus. Or maybe, it’s something entirely different. It’s really too early to say.

In the meantime if any of you have had brindle dogs test positive for Dominant Black I’d like to hear from you! Please comment with your test results and breed.

Candille, S., Kaelin, C. & Cattanach, B. A β-defensin mutation causes black coat color in domestic dogs. Science 318, 1418–1423 (2007).

Ciampolini, R. et al. Characterization of different 5’-untranslated exons of the ASIP gene in black-and-tan Doberman Pinscher and brindle Boxer dogs. Animal genetics 44, 114–7 (2013).

Oguro-okano, M., Honda, M., Yamazaki, K. & Okano, K. Protein Genes , and Their Association with Coat Color Phenotypes in Akita-Inu Dogs. (2011).

Comments

I have Japanese Akitas (not American Akitas). They come in three color varieties, of which I have all three: red, white, and brindle. I have done A Locus, E Locus, K Locus, and S Locus tests on them as appropriate. Additionally I have paid for a fellow breeder to test her dogs and help confirm a hypothesis I had.

A Locus: All were homozygous ay,ay.

E Locus: Each white tested as homozygous e,e. Studs and dams known to produce white puppies tested as heterozygous E,e. None carried Em but not surprising since the breed does not have black masks.

 K Locus: Three brindle dogs tested as heterozygous Kbr,ky. Two of those dogs have sired red offspring (the third has not been bred yet). One white dog with two brindle parents tested as Kbr,Kbr. An other white dog with two red parents tested as ky,ky and she has had red, white, and brindle offspring when bred to a brindle male carrying E,e. None tested positive for Kb.

S Locus: All were homozygous Sp,Sp.

I forgot to add, one white dog with a white mother and red father tested as Kbr,ky. That dog has a brindle grandparent on its mother's side.

I have border collies, and while brindle is less an issue in the breed, I had a litter 18 mos ago, from 2 classically marked black and white parents, in which all the pups were born with what can only be described as a wolf silver sable color, that eventually grew out to a near solid, near black color on all puppies (pigment still appears to be off--dark grey skin pigment and auburn coloration in the top coat--they now look like what some in the breed call "seal" colored). What is insteresting is that testing DNA for two of the four showed KBKB, with the added surprise that at the A, one pup is ayat, the other is away. To add to this, a half sister (by sire) to the dam of this litter also recently had a "silver" litter, after having a normally colored litter to another stud (While they share a sire, the dams of the dams, and the studs used to each, bear no immediate relation). Many things are insteresting about this--first, the presence of aw in border collies, and secondly, that some other process temporarily affected the coloration of the entire litter (not just the ones(s) carrying aw) such that they were all darker and lighter variations of a grey/silver wolf color. These litters are extremely rare--I am aware of only 3--and are popularly called chinchilla litters because of the appearance of the coat in the young puppies. So, not only can a heterozygous dominant black be incomplete, so, too, can a homozygous dominant black show a phenotype that does not necessarily relate to what's hidden at the A. (the two pups tested also showed BBDdEe, and BBDDEe)

I have a Staffordshire Bull Terrier, who is OBVIOUSLY brindle and who was recently DNA tested for colour.

A-LOCUS AGOUTI (AFFECTED)

B (TYRP1 LOCUS) BROWN/CHOCOLATE (CARRIER (Bb))

DILUTE COAT COLOUR MLPH GENE (BLUE/GREY) (Normal (DD))

K-LOCUS (DOMINANT BLACK/WILD TYPE) ( Carrier K/k wild type)

EM-LOCUS MELANISTIC BLACK MASK ALLELE (Carrier (E/Em))

E-LOCUS (EXTENSION - YELLOW/LEMON/RED/CREAM/APRICOT) (NORMAL)

I had recently three brindle Berger des Pyrenees tested and they all were k/KB on K-LOCUS, two of them were ay/ay one was ax/ay on A-LOCUS. I was very surprised, because I always thought the brindle should be kbr on K-LOCUS. I could not find a lab which could test for kbr, do you know one? I would like to make sure if there really is no kbr. 

There is currently no lab that tests for Brindle.  The mutation or mutations have not yet been located.  It is possible there is more than one brindle mutation.