I wanted to point out that as of this date, there has not been a 'White' gene associated with dogs. It has been found in other species of animals, but not in dogs.Originally Posted by NicoleLJ
In all mammalian coat color genetics, there are only two types of pigment. One is Eumelanin (which codes for "true" black or near black) and phaeomelanin (which codes for biscuit, to red, an brown/tan colors). True "white" is the absence of pigment granules in the hair.
In dogs, "white" color in several sable/agouti breeds (in the A series) is caused, in part, by a recessive form of the extension gene (E series). Only dogs carrying at least one dominant allele for E can have black in their coat. So the double e (e/e) derails the formation of black pigment (eumelanin) in the hair at the melanocortin-1-receptor. This affects the formation of black pigment in the *hair* only -- e/e dogs will always have pale colored whiskers, they cannot have black hair at all.
Colloquially, the e/e combination is sometimes called "recessive red", this is because a fully pigmented dog can only have two types of pigment, black or red. That colloquial name can confuse the matter because the gene involved with e/e regards black pigment. So if the dog is not black, it can only be red if it is fully pigmented.
So what if you or an animal you have is e/e? Having lighter color recessives which permit expression for blonde or red hair, just means you do not have the genetics to form the blackest form of pigment in your hair strands. Has nothing to do with albinism or your dog being genetically disfigured.
Albinism: True albinism alleles are associated with the "C" series (on Tyrosinase gene), which controls Color ("to be or not to be"). The C series as it affects phaeomelinin (and eumelanin to some degree) in other animals, has not been shown to exist as originally expected in dogs. For example the 'chinchilla' allele c^ch which Dr Clarence Little had theorized. Tyrosinase (the gene controlling expression of these traits) may or may not still be implicated but it just hasn't been resolved in dogs to date. GSDs and other white sable breeds would be capital "C" in this series because they ARE fully pigmented dogs. They just have a protein that merely affects the pigment granules in their hair.
Another gene associated with white, is the Merle gene - and this one IS directly implicated in birth defects. This gene is not found in purebred GSDs (nor ASDs).
Pinto alleles do not concern purebred GSD so we won't get into that here.Although an interesting mutation has occured in the GSD - "Panda Shepherds" which have been DNA'd and are truly a mutation.
To date, it is not known what turns off the phaeomelinin (biscuit, red to brown) in e/e breeds that are "white" instead of red. But e/e has certainly been implicated as part of the factors that produce "white" sable breeds.
Typical e/e breeds are Golden Retrievers and yellow Labradors. You never see solid red (or yellow) GSDs or Anatolians - if they are reddish, they will also have black hair and that means that they are not "recessive red" (also called 'clear red'). This is because another unidentified gene also at least partially derails the complete formation of the second pigment, phaeomelanin. Sometimes these "white" breeds, like the e/e breeds will have a little more biscuit color to the edges of their ears. Phaeomelanin is temperature sensitive and cooler areas of the body will sometimes appear darker.
Scientists involved with the genome studies regularly report their new findings. Sometimes it is a little bit hard to follow if one doesn't have the background or sheer determination<g>.
A very useful site to read about pigment studies in dogs is here: http://homepage.usask.ca/~schmutz/dogcolors.html
Having said all that, people create breed standards based on an 'artist's conception' of conformation to manmade ideals of perfection.
My thoughts on this is that since the agouti/sable colored breeds as I know them, have banded hairs. See pic:
When the dog gets a double dose of e/e, it affects the production of the banded pattern - because both eumelanin and phaeomelanin alternate in agouti hairs normally. Since the black pigment doesn't ever turn on, it somehow results in hijacking of the production of the pigmented coat pattern, thus giving us the "white" (or cream white) colored hair. This is just my own conjecture, because in these sable breeds, if there is an additional allele that is involved, that only turns off red or dilutes red, that would mean that this stray gene would sometimes occur in it's recessive or dominant state separate from the state of the allele in the E series. That might mean we could see white GSDs with black masks if this separate gene worked in a typical autosomal diploid manner. Since this doesn't happen, I think that something in the banding pattern of the A series gets hijacked when the E series is in a recessive state.
The hair snapshot above is from an Anatolian female (the center dog in my sig). This female has "white" ancestors in her pedigree as do many Turkish dogs.
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