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PostSubject: Tri gene   Tri gene EmptyMon Sep 28, 2009 5:19 pm

"Hey! That Dawg Don't Look Purebred..."
An explanation of the tan-point pattern sometimes seen in the American Pit Bull Terrier
by Ed & Chris Faron

Just where does the black and tan "Rottweiler looking" pattern come from, and is it a sign that an APBT is not purebred? Since this color pattern pops up more frequently in our bloodline than in some others, we have been asked about this on quite a few occasions. We thought we would take the time to write up a short article explaining this color pattern, how it is inherited, and where it comes from.
The tan point pattern is caused by a recessive gene on the Agouti series gene locus, the following are the alleles (variations) that are definitely known to occur in the American Pit Bull Terrier. There are also a couple of other genes on this same locus, but they are most likely not present in this breed, so we will ignore them in this article to try and keep things simple.

A 14 week old black & tan APBT puppy. Though unusual-looking, this pattern is a perfectly natural coloration for a Pit Bull.

Agouti locus alleles present in the APBT A Dominant Black: produces a solid color (ie.black, chocolate or blue) *see note below
ay Dominant Yellow - Produces reds and buckskins
at Tan-Point (recessive)- produces solid color with tan 'points'

*Note: There is strong evidence to suggest that there are either two separate genes causing a solid black coat, or possibly even just one gene that is NOT on the agouti locus, but that is a whole different matter we'll save for another article. If black is in fact not an agouti locus gene then Dominant Yellow should be expressed as Ay instead of ay.

A dog needs to inherit two copies of the tan-point gene to be a black & tan. If a pup inherits one copy of the tan-point gene and one copy of the dominant yellow gene, which causes a red or buckskin coloration, then the dog will be red or buckskin, not black and tan. If the dog inherits one copy of the tan-point gene and one of the dominant black gene, the result will be a solid black dog. Because of the recessive nature of the tan-point gene, it can actually remain hidden in the gene pool for many generations without expressing itself. In the case of our breed (where this is not a common color) this is what often happens, but it is important to realize that when the tan-point pattern does pop up it is not some new color mutation that appeared out of nowhere, but rather the manifestation of a gene that has been present in this breed all throughout the known history of the American Pit Bull Terrier. Though it is impossible to say for sure where the coloration originated, our best guess would be that it came from some sort of terrier blood that was introduced many, many years ago, probably during the early formation of the breed in the British Isles.

Actually, part of the reason the color is uncommon is that there has been a distinct prejudice against it by many people, either because they feel it is not a typical Pit Bull color, or even actually thought it was the result of a mixed breeding. The latter reason shows an ignorance of basic genetic principles, because the gene is recessive, there is no way you could breed a Rottweiler or a Doberman or Manchester Terrier to a Pit Bull and get puppies with the tan-point markings unless the Pit Bull was carrying the tan-point gene too. If in fact the black and tan color was not present in the APBT gene pool, you would have to breed to a dog of another tan-point breed, and then breed two offspring from such a breeding back together to get black & tan dogs, in the first generation you would get no tan-pointed offspring.

The tan point gene does not actually create a black & tan animal, the gene itself does not produce any color but rather a pattern of a solid color with light-colored 'points'. These 'points' always appear in specific places but the actual size and distribution of them is somewhat variable. The exact coloration that is produced by the tan-point gene is dependant on the color genes present at other loci, for instance if the pigmentation is black, the result will be a black & tan, but if the dog's pigmentation is chocolate or blue then the pattern would produce a chocolate & tan or a blue & tan, respectively. A few of the possible tan-point variations seen include the following:

Black & Tan
A classic black & tan. This particular dog also has white markings -- the black, tan & white combination is also known as 'tricolor'.

Chocolate & Tan
When the tan-point pattern is coupled with red/red nose (chocolate) the result is chocolate & tan.

Black & Buckskin
When combined with buckskin instead of red, the pattern creates a pattern of much lighter points; with extremely pale buckskins the coloration might even be mistaken for black & white at first glance.

White markings are caused by an entirely different set of genes, and appear the same way on a tan-point dog as they would on any other color, if present -- a tan-point dog may even be spotted, in which case the spots would be two different colors depending on whether the spots were over areas where the tan-point pattern was present. Brindling, if the dog is a brindle, will only be seen in the tan points, in fact if the tan-point dog is very heavily brindled then the brindled areas may make the dog appear to be a solid color instead of a tan-point.

(We have a couple of photos of brindled black & tans and brindled chocolate & tans but are still looking for them at this time, we will scan them and add them to this page when we find them.)

Another interesting thing to keep in mind is that the dominant yellow gene does not always mask the tan-point gene entirely; this is known as 'incomplete dominance'. With incomplete dominance, a buckskin or red dog that is carrying the tan-point gene will have the tan-point pattern visible in the form of a pattern of black (or chocolate, or blue) hairs mixed into the coat in the places a tan-point dog would have been solid colored. This is referred to as 'sabling' in most breeds. Here are a couple of examples of sabled APBTs:

A reddish-buckskin bitch with black sabling. The amount of sabling seen varies from dog to dog, in this case it is quite pronounced, resulting in a mask pattern on the face, etc.
A red bitch with blue sabling. This is an interesting combination because by carrying both the tan-point and blue genes (both rare) this bitch if bred to a male with the same make-up could possibly produce blue & tan offspring, a color (to the best of our knowledge) previously unheard of in the breed. (The puppy in partial view on the right is a black-sabled red)
A brindle bitch with black sabling -- the sabling is less noticeable because of the stripes (and also the black mask this bitch has) but the pattern can still be seen, especially in the face area -- note the 'points' over each eye.

Our own first encounter (besides seeing pictures in various books) with a tan-pointed APBT was a litter we had off a half brother-sister breeding off a son and daughter of our old Bandit dog. Bandit himself never threw a black & tan, because the bitches we were breeding him to (mostly Nigerino, Honeybunch, and Snooty bitches) did not carry the gene. He did throw a fair number of sabled pups, but at that time we were not that familiar with coat color genetics and it never occurred to us that these "dirty buckskins" as we called the color, were caused by the tan-point gene, as we had never seen a tan-pointed APBT firsthand. Then out of Renegade and Maggie came a litter of blacks and brindles -- and one big male marked just like a Rottweiler, except with brindling in the points. We picked him as our keeper because we thought his coloration was a novelty, in fact we named him "Wilside's Devil Dog" (call name Pitweiler) as a joke because of his markings; this attempt at humor would later cause us a bit of aggravation when someone who saw Pitweiler spread a rumor that we had a pet Rottweiler and were crossing it into our APBTS...

Anyway, Pitweiller was the first of numerous black & tans we have had since, plus a few chocolate & tans. Most of them came from doubling up on Bandit in some way or another, except for one breeding to an inbred Ch. Booker T bitch we made with Rapid Roy that resulted in a litter of mostly black & tans. We have also seen tan-pointed pups from several other bloodlines, so while the gene is fairly rare it is probably a lot more common than most people would think. Whether you find the tan-point pattern interesting and appealing, or think it makes a dog look like a "mutt", the fact is it has been a part of our breed for probably well over a century, and will continue to exist.

We ran a query on our CompuPed database of APBTs (30,200 dogs at this point) on all dogs with a known color who were tan-pointed. Click here to view the results.
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PostSubject: Re: Tri gene   Tri gene EmptyMon Sep 28, 2009 5:25 pm

Great post it will explain to a lot of people how color genetics work. We should also find a color wheel also to show how color patterns are formed. I have seen a couple posted on the net but can't remember for the life of me where at. I will try to look for those.
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