COAT COLOR GENETICS
This is my understanding of the facts concerning the color
genetics of our whites. Since we call this list "White Shepherd Genetics" it seems appropriate that we speak of the color genetics responsible for our pure white dogs. To those of you who are already well informed in this area, my apologies for a rather "boring post". I hope the post is readable as I had great difficulties in getting it to correctly format in the plain text that the list allows.
We must, of necessity, start with the GSD, and the genetics relevant to his color patterns if we ever will understand how we arrive at our whites.
First the basics: Each GSD has a series of genes responsible for their various colors, markings, patterns, etc. These are arranged in a chain and are represented by letters "A" through "T", with each letter standing for a "locus", or "location" in that chain - with some other possibilities not yet well understood. This chain resides within all the chromosomes coming together forming the very cells that the animal is built of. So, these genes are in each and every part of the animal from brain cells to tail cells, (including the hair follicles which produce the coat) and the chain responsible for colors would look something like this:
A -- B -- C -- D -- E -- F -- G -- I -- etc. (simplified)
| | | | | | | | |
A -- B -- C -- D -- E -- F -- G -- I -- etc. (simplified)
Each locus above is responsible for certain characteristics concerning colors and markings and there are TWO genes, or alleles at each locus, one is derived from each parent. In the reproductive cells of the dogs, eggs and sperm, there is only one allele from each locus present, and when the sperm meets the egg the other allele from the same locus in the mate's gene joins the single one creating a new pair for the beginning offspring. Each allele of the egg and sperm can be different at each locus depending on the characteristics of each parent. In addition to that very simplified drawing above, there exist sub-alleles within the groups above that are the real modifiers and determiners of the colors and patterns of that offspring. Note that similar genetic processes and chains exist for ALL of the characteristics concerning the dog, not only color and pattern, but eyesight, disease potential, hips, etc.
Now a little deeper, and in order of dominance:
The "A" (AGOUTI series) locus.
In GSD's only: (Other alleles exist in other breeds)
ay dominant, (sable or gold sable),
aw (gray or silver sable),
as (saddle marked),
at (bicolor) and
a (solid black).
The "B" (BLACK series) locus,
B, dominant, (black pigment),
b, (liver or brown).
The "C" (COLOR series) locus,
C, dominant, (full color),
cch,(partial albinism, but little effect on pigment of
cd, ***(Pure White coat with dark eyes and nose.)***
Note that both cch and cd will have no effect in first generation offspring unless in a homozygous state (TWO OF EACH).
For simplicity, skip now to:
The "E" (EXTENSION series) locus,
Em, dominant, (black mask),
E, (dark pigment but no mask),
e, (clear red or tan), ("in the homozygous state causes black hair pigment to convert to tan").
The "I" (INTENSITY series) locus,
Int, dominant, (dilutes tan towards a dirty white),
intm, (dilutes tan towards light yellow),
int, recessive, (no dilution).
That is not nearly all the detail, there is much more than I know, let alone being comfortable to post, but it is enough to show some examples concerning the possibilities with the story of White x White = Dark. **(Which is genetically NOT possible with pure whites)** Additionally, please note that we are speaking here of the overall colors and patterns of the dogs, NOT any specific black or colored mark on an otherwise White dog. Such marks have very different reasons for occurring, some may be genetic, and others are not.
Example 1, Genetic color combination of a typical, masked, sable GSD from the above listed loci.
(ay-??) - (could be ay, aw, as, at or a - and still the dog would BE sable since ay is dominant),
(B-?) - (could be either B or b and still the dog would HAVE black pigment in nose and toe pads since B is dominant),
(C-?) - (could be C, cch, or cd, and still the dog would BE fully colored since C is dominant)
(Em-??) - (could be Em, E, or e and still the dog would BE masked as Em is dominant)
(int-?) - (this series is more difficult since *complete* dominance here remains not yet proven), int - int would give no color paling while Int - int would show some and Int-Int would show maximum color paling.
Note that the recessives, shown as possibilities above, could very well be the exact gene donated to any offspring of this dog and would therefore show up in the second generation.
Example 2, Genetic color combination of a typical pure white dog as we know it here from the same loci as above.
"A" locus, any combination here, (ay-ay), (ay-as), (aw-at), (as-a),It does not matter, but still the locus and genes there exist.
"B" locus,(B-?) - (could be B, or b and still nose and pads are black in first generation),
"C" locus, ***(cd-cd)*** is the **ONLY** possibility for a true pure white. As the most recessive two alleles at this locus these two in homozygous combination mask whatever the "A" series was trying to create, as well as whatever is happening at the E locus, and since there can be no color paling in a pure white dog as there is no color, no importance is placed on whatever resides at the I locus, but these alleles still do exist.
At this point I note that when we speak of a **COLORED, WHITE FACTORED DOG**, we are describing any colored dog that has at the "C" locus, just ONE cd, like (C-cd), or (cch-cd).
Such a dog can be colored just as the darker parent with no effect from that one cd since it is recessive to C and cch, but this dog is **capable of producing pure white pups**.
The same for a **BLACK FACTORED DOG**, this dog has at the "A" locus, just ONE a, such as (ay-a) or (as-a) or (at-a).
Since a is recessive to ay, the dog is a sable, saddle, or bicolor but capable of producing solid black pups.
Remember, even a **solid white** dog still possesses these same Agouti series alleles, but his (cd-cd) at "C" has masked them. They are nonetheless present and genetically viable.
If the dog has both ONE a, at the "A" locus, and ONE cd at the "C" locus, it is **BOTH WHITE FACTORED AND BLACK FACTORED** and therefore capable of producing its own color, or white, or solid black, depending on what gene arrives from the mate and how the two pair up during reproduction.
Example 3, Genetic color possibility for a dog that might appear nearly white, but not the true white that we know on this list. More of a dirty or gray or yellow white color that might look whiter if cleaned, or even *bleached* with peroxide. (Sorry to mention "bleached", but documented accounts of this happening are available.)
"A" locus, could be any combination, arbitrarily, aw-at (would be gray or silver sable with a recessive for bicolor)
"B" locus would still be B-B, or B-b,
"C" locus, could now have cch-cch, and even though masked,
"E" locus, could have E, or e rather than Em - (no mask).
"I" locus, could be worst case for paling
Int-Int. (maximum dilution of tan to dirty white)
Now this dog looks nearly white to many who are not as familiar with whites as some of us, but if bred to a pure white bitch, would produce **NO** pure whites since he has no cd at "C" to donate to the one cd received from a pure white bitch.
The offspring would therefore be either aw, (gray sable) or at (bicolor) from him, and whatever "A" series alleles the bitch carried in masked form perhaps aw-as, (saddle is recessive to sable, so in this case that pup would BE sable) and, bicolor is recessive to saddle, so if the pup received (as, from the bitch, and at, from the dog) it would BE saddle.
"C" they would all be cch-cd,(cch from the dog, and cd from the bitch)- White factored, but not white.
"I" they would receive one Int from the dog and one "I" series from the bitch,
All some form of faded or paled (from cch and Int) sable or saddle marked and some with no mask (from E), (all would be white factored - from the one cd received from the bitch), but none even as white in appearance as the original dog may have been.
If instead, the dog had (cch-cd) at his "C" locus, and e-e at the e locus, he would appear nearly white, but not pure white and could produce about 50% white pups together with about 50% faded colored. If the dog had (aw-a) at his "A" locus as well, he could produce solid black, if the bitch as well carried (?-a) at her "A" locus. But in all likelihood, this black would be a faded black with bleed through and not endure past youth due to the effects of the "I" locus of Int and its paling tendency.
Below is a link to a page created by Rhonda McMahan from Surefire specifically to point out what such a dog might look like:
Note the dog on the left is a gray, or silver sable, but has almost no black, however, does have the mask from Em at his "E" locus. The bitch on the right is an example of a dog carrying E(no mask) rather than Em. It is easy to see how if the dog on the right had inherited E, rather than Em at his "E" locus, then he would have no mask and show nearly no dark or black at all, but is nevertheless a sable dog. In the case of this dog, some whites could be produced if put with a pure white bitch, since it is known from his parentage that he does carry one cd at "C", but if he did not, then with a pure white bitch would produce **NO WHITES**. If his owners had cleaned him well and perhaps used some peroxide prior to the picture, he could easily be termed a white and put up for stud as such to people& less familiar with the correct appearance of a pure white.
To end this complicated post, a summary.
To BE a **pure** white, the GSD **MUST** possess two cd's at the "C" locus, as (cd-cd). These have MASKED all of the Agouti series patterns at "A" and all of color and masking effects arising from "C" and "E", and have made whatever is at "I" irrelevant since we can't see it. This dog will produce **ONLY WHITES**, IF PUT WITH ANOTHER HAVING THE SAME TWO cd's at "C" locus. Note that in this scenario, the sex of the parents is of no importance the need for two cd's at"C" applies to either sex.
HOWEVER; the same pure white, if put with a NON-WHITE factored, colored, will produce *NO WHITES*, but all pups will then be white factored. In the case of this mating with a non-white factored colored, the offspring will now display what was "masked" at the "A", and "I" locus of the white, and will have any Agouti series pattern as well available from the colored and possibly very paled colors from the effects of "I", unseen, in the pure white parent.
And finally, two coloreds, both white factored, (one cd each at the "C" locus), will produce approximately 25% pure white pups and 75% colored. This would be expressed as C-C, C-cd, C-cd, cd-cd.
For a much more thorough read on how this all works, including pictures of each visit:
Please note that there are **5 ** pages to the whole story, accessible by clicking on the *red dots* at the bottom of the page. Our white dogs are described beginning at the bottom of page two, and then on page 3.
*references for the above include those from the book, "The German Shepherd Dog", "A Genetic History", Dr. Malcolm B. Willis, 1991, as well as much passed on to me from a very knowledgeable breeder, Rhonda McMahan at Surefire Shepherds, also a prominent list member here. Feel free to visit Rhonda's web site at http://www.surefireshepherds.com or mine, at http://www.marshcreekcellars.com
Jim Glassmoyer, from Marshcreekcellars