COAT COLOR IN THE TOLLER: Breed history and current genetics.
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Now that we've discussed the many ways red can be expressed genetically in the coat of a Toller, it's time to take a look at buffs, white markings and nose color.
BROWN LOCUS: Brown is the recessive gene that has been romantically called "chocolate" in some breeds and is also called "red", "liver", or "brown" in various other breeds. The dominant allele here produces a black dog, the recessive results in a brown dog. Actually it turns out there are at least three different recessive brown mutations here but they all cause the same coat color change. This gene is formally called Tyrosinase Related Protein 1, or TYRP1 for short, and is found on canine chromosome 11. Again, this sort of "alphabet soup" name means that the gene and its action are known.
Tollers can have black or brown noses, so both the dominant here and at least one of the brown recessive alleles exists in our breed. In Tollers the nose color is described as self or black. Most of the "self-colored noses are probably recessive brown. Even the black can be confusing since it can fade.
- B = Dominant allele that allows for a fully pigmented (black) dog.
- b = Recessive that permits the expression of brown (chocolate, liver, red) dilution.
Brown dogs (brown nosed dogs) are, quite literally, bleached in pigment at the molecular level (eumelanin is unprotected from hydrogen peroxide). This diluter gene works particularly on eumelanin (black) pigment; phaeomelanin (red) pigment is not affected. So in clear red Tollers this gene just affects the nose, eye rims and lips. However in sable Tollers that are not homozygous for clear red, the sabling will be brown rather than black.
Those blasted buffs
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The two buff puppies in the litter can be easily distinguished from their littermates. |
This three month old buff pup has very light eyes and his skin and fur appears to be bleached or faded. |
DILUTION LOCUS:
This is the gene that results in the blue Doberman and the blue Dane and probably causes buff in Tollers. The dominant allele here allows for full expression of color in the coat and the recessive produces a diluted color. Thus, a buff Toller is the product of two Tollers tha carry the recessive dilute color gene allele. The color is present at birth (i.e. it's not a graying gene, where the dog “fades” as he matures). Dilute dogs have lighter colored noses and lighter eyes than their normal littermates. The change in color is caused by a change in the distribution of the pigment within the hair. Dilute dogs have clumps of pigment rather than a smooth even coating. Dilute is not related to pattern, so any dog of any color, including the shaded (sable) Toller, can "show" dilute.
- D = allows for black pigment to form.
- d = produces blue/slate/gray dilution.
This gene affects skin and coat color simultaneously. Buff Tollers appear to be dilute in that they have lighter eyes and noses and lighter hair color than their littermates. Some breeders have reported a dilute puppy that grows up to appear normal. Since there is a test available for dilute, it would be interesting to test dilute Tollers to see if the ones that darken have the same mutation as the ones that stay light colored. Again, testing for color genetics is available through Healthgene or Vetgen for a reasonable price.
Adult Buff Tollers
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Here is that same pup as an adult. While his eyes are no longer a bright blue, notice how light they still are. Also notice his fur. It's almost as if he has been given a silvery overlay. |
When pictured alongside of a non-dilute Toller, a Toller Buff appears to be faded or bleached. |
The troubles with white: too much, too little, or just right
SPOTTING LOCUS: This is the traditional location of recessive white spotting patterns present in many dog breeds, including Tollers. There may actually be two or more loci involved in recessive white spotting, however tradition has placed the alleles together at the S locus. There are four alleles and incomplete dominance postulated to explain the variations seen in dogs. The truth may in fact be more or less complicated. It is an active area of research because of the association of white spotting with deafness in dogs, mice and people.
This series goes from solid to white. There can be heterozgyotes: intermediate hybrids in pattern with one more dominant and one more recessive gene that produce an intermediate phenotype that is deceptive as to breeding capacity, plus there is always some range for each gene in question. The most likely alleles present in the Toller are shown below
- S = allows for self-colored dog: no more than 10% body white confined to the toes and chest even when full expression of white is present.
- s^i = "Irish pattern": produces an extension of white from 10% to 30% in a symmetrical pattern involving some or all of the following areas: feet/lower legs/belly/chest/tail tip/collar/muzzle and blaze. Recessive to S, this locus demonstrates incomplete dominance, so intermediate types appear in heterozygotes.
The problem for Tollers is the breed standard disqualifies dogs with a white collar or other “excessive” white markings, and these can be part of the expression of “true-breeding” “Irish” dogs, ie. Irish homozygote. So, while the SS homozyte is going to always produce a dog nearly solid, and the S/s^i heterozygote (“Irish hybrid”) will likely always produce a dog within the standard, in it’s full range, the Irish allele can produce too much white on a Toller to meet the standard.
Note that nose color is NOT inherited separately from coat color, and in fact it is a well established principle of coat color genetics that nose color largely INFORMS as to coat color. Nose/skin color is a huge clue as to what coat color genes a dog has inherited. That said, again, inheritance is not monolithic and so not every aspect of every physical feature is purely and directly inherited after all. So as to skin color, especially with brown dilute dogs, the shade of the nose/eyerims can vary from bitter chocolate a fleshy tone, never mind some changes in nose color (again, especially with dilute colors) are seasonal, medical or what-have-you. Nose/eye rim color (that is SKIN color) in dilutes tends to appear a bit lighter than coat color; it can be the same, but is never darker. Eye color with diluter genes is also affected (lighter than black pigmented equivalent littermates, for example). So called "modifiers" are irrelevant and beg the case anyway (i.e a "modifier" is a separate gene with it's own function and interdependence in genes is anyway commonplace, so this term as absolutely no real meaning and was therefore discarded from even relevant lay discussions in the past decade). Eye color is affected by coat color genes, but also has its own dynamic.
CONCLUSIONS:
As Toller owners and breeders we usually don't think of our dogs as being anything other than red or occasionally buff. We are all aware of the fact that there is more than one way to reach that beautiful red we see in our adult dogs. Many of us have kept a watchful eye on our sable pups waiting for the dark masks and tails to fade into a beautiful rich red. But, as you can now see, there is a little more to this business of being red than meets the eye. Our little red dogs seemed so simple, but in fact their red coat color comes from 3 different red genes. What this gives us are four genetically distinct colors: clear red with a brown nose, clear red with a black nose, sable red with a brown nose and brown overlay and sable red with a black nose and a black overlay.
Given the health concerns we have for our breed, color receives little attention when it comes to genetics, mostly because, to us, these guys are just little red dogs. Given the fact that the history of our breed contains a number of different breeds including herding breeds and sporting breeds, it makes sense that we reached our current state of red by adding a number of different types of red into the mix. We are used to thinking about whether our dogs have black or brown noses and some of us might even have preferences. With new color genetic testing available for other breeds it would probably be easy to put together a test kit for Tollers where those who have preferences as to sable-red vs. clear-red, and/or brown noses, vs. black wouldn't have to experiment or guess in their breeding programs. Breeders could also test for dilutions like D to avoid producing buffs in litters where this might be a concern.
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