Brindle -- question for the genetics wizards - Page 1

On the topic of brindle... I'm trying to understand something.

I know that it's on the K locus, however I'm wondering the difference between dominant black which -would- mask the brindle gene. Dominant black is located on the K-locus.
The K-locus has three genes; K=dominant black, k(br)=brindle, and k = non-solid black which allows the A locus to be expressed.

The GSD is one of the few breeds that has recessive black, located on the A-locus. Sable is also located on the A-locus.
The A-locus is as follows: A(y) = sable, a(w) = agouti (which looks like sable), a(s) =saddle pattern, a(t) = tan points, and a = recessive black


The Belgian Terv is supposed to carry both forms of black. I believe labrador retrievers do as well because I used to work with them, and brindle occurs, albeit infrequently, in purebred labradors. Sable and brindle could theoretically co-exist together in genotype, but I don't know what the resulting dog would look like. Recessive black can be expressed only if both parents carry the gene... Dominant black will be expressed if only one or the other parents is black.




So my question is: how can it be proved (or disproved) that certain workinglines could carry dominant black, and therefore express brindle on rare occasion? Can it be proved that dominant black, which is typical for most breeds, with rare exceptions like the GSD, does not exist in GSD bloodlines?

I am by no means an expert but I suspect it comes from the sneaking in of Dutch Shepherds being done by breeders IMO

j.c.carroll,
according to Malcolm Willis (1991), the brindle gene is located on the E or Extension Series. It is called e-br. See page 40/41 if you happen to have his book "The Genetic History".
Chris

Got to admit, a brindle German Shepherd (I know Dutchies are out there already) will look mean and ideal for true work. If someone ever decides to give this gene cocktail a try, let me know where to send my deposit.  What the heck, with all these other colors out there, why not a brindle? Relax everyone, just food for thought, don’t go missile lock on me, lol.

JC, fisrtly the A locus. 

A^y - sable
a^w -  wolf sable (GSD 'sable')
a^t - tanpoint (B&T, saddle, bicolour)
a - recessive black

This is the most recent designation for the A locus according to Schmutz and a paper detailing the research into this is pending.

There have been a few threads on here citing anomolies that could be explained by the presense of dominant black in the breed, but they could also be explained in other ways.  It could never be proven that dominant black didn't exist, well, not unless all blacks and white/creams (and all dark sables and dark B&Ts, to be sure) were DNA tested for it, but it could be proven to exist if found by DNA analysis of suspect cases.  There is now a DNA test for the K locus at HealthGene.

The presence of dominant black in the breed wouldn't increase the liklihood of brindle being present.  I hope I have understood correctly that that is what you assume?  The reason for this is that brindle needs phaeomelanin pigment (tan/red/yellow) to express and this only occurs in tanpoints and clear sables in the GSD.   I have to add here that whites are also phaeomelanin pigmented but the action of recessive ee prevents the brindle stripes from expressing.

Brindle is always dark stripes on a phaeomelanin (light pigment) base colour, not the other way round.  A dog could be solid black and genetically brindle but the striping wouldn't show because it's black on a black background.  So, a recessive black, genetically brindle dog (aa k^br ), would be a brindle carrier, and so would a dominant black that was K k^br Both of these could pass on the brindle allele to their tanpoint offspring where it would be expressed as black & brindle  a^t k^br.

So, both dominant black and recessive black can carry brindle unseen. If brindle did still exist in the breed, it would very likely have shown up considering that B&T is by far the most common colour pattern.  The only way it could be carried unseen through the generations is if there was an unbroken line of solid blacks (dominant or recessive) and/or whites.

Hope that makes some sense.

"The Belgian Terv is supposed to carry both forms of black. I believe labrador retrievers do as well because I used to work with them, and brindle occurs, albeit infrequently, in purebred labradors. Sable and brindle could theoretically co-exist together in genotype, but I don't know what the resulting dog would look like. Recessive black can be expressed only if both parents carry the gene... Dominant black will be expressed if only one or the other parents is black. "


Just got to comment on this bit too :)

A normal, all over brindle eg Boxer, Great Dane, Dutch Shepherd, is sable plus brindle - A^y k^br.  As explained above, brindle needs the phaeomelanin base colour from the sable allele, to allow the dark stripes to express.

I've never heard of recessive black being present in Labradors.  I think it very unlikely.  Almost all Labs are homozygous KK.  It's the low frequency of k^br and k^y in the breed that allows the occasional ocurrence of tanpoint, brindle tanpoint (black & brindle) sable and brindle to occur.

Dominant blacks do usually have a black parent but it's not essential.  There are genes at other loci that can override it.  Recessive yellow (ee) for instance.  Eg a white/cream mated to a sable could produce dominant black.  Also merle can 'diguise' black.  Then we have the other genes that dilute black - brown, blue, lilac.  There are probably others too but I can't think just now.....

Ah, okay. That makes sense. Thankyou, Pod. That clears it up all quite nicely ^_^

The biggest hurdle I seem to have with genetics is keeping up with the latest news. To be honest I never studied the genetics in labs; just took it for granted back then.

Thanks for the thorough reply. That answered my question perfectly.

Oh,   WoW  !! 

Good  OL   fashion Genetic topics !!

I Love IT !!! 

 So,   If Black on Black Brindle is hidden, Is it possible for the Dominant black to also play a role in the delayed expression of Bi-color ?     The bi-color that is not detected at all until the dog turn around 2 yrs.  

No I don't think so Jamille.  The extent of dark and light pigment on B&Ts is probably more to do with the, as yet unidentified, gene/s that controls this.  It could be that the E locus, that includes the mask allele, has some influence on this as dogs with strong mask also tend to have tarheels, toemarks etc.