THE ALBINO LOCUS

The C locus is where the albino gene is located in most animals. C locus genes are thought to affect the intensity of pigment, particularly phaeomelanin (red).

There are generally thought to be at least four genes on the C locus:
C - Normal pigment
c^ch - Chinchilla
c^e - Extreme chinchilla (extreme dilution)
c^p - Platinum (ivory)

CHINCHILLA, EXTREME CHINCHILLA AND PLATINUM

Chinchilla causes dilution of red (phaeomelanin) pigment to a lighter shade of tan or yellow. Eumelanin (black, liver, blue, isabella) is not affected. Extreme chinchilla causes further dilution, usually to cream or light yellow, and platinum is dilution to white (usually with a slight yellowish sheen).

Very little is known about these three genes. It is possible that they display incomplete or co-dominance, which would account for the extreme variations in shade. A c^chc^p (one copy of chinchilla, one of platinum) dog would therefore appear to be around the colour of a dog with extreme chinchilla (c^e), but possibly slightly darker.

The chinchilla series is thought to be responsible for solid white dogs with black nose/lip/eye-rim pigment, such as Samoyeds. These dogs are recessive red (ee) with the platinum gene, which dilutes their phaeomelanin (red) to white. See the Schnauzer section below for more information about white.
Genetic testing on Samoyeds has found them to be homozygous for both recessive red and recessive black. Some geneticists (such as Sue Ann Bowling) have suggested that it is this combination of genes which causes them to be solid white. This would be because recessive red stops the dog from producing eumelanin (black pigment) and recessive black stops it from producing phaeomelanin (black pigment). The result would be a dog that couldn't produce any pigment at all in its coat, and so would be solid white (but with a fully-pigmented nose, because recessive red only affects the coat and not the nose, eyes etc). This is certainly an interesting theory, but there are a few problems with it. Firstly, some Samoyeds have "biscuit" spots, which are small patches of cream, and some are even cream all over. This would not be possible if the dog could not produce phaeomelanin, because cream is very diluted phaeomelanin. This variation suggests that the white on Samoyeds is simply dilution and not due to the recessive red/recessive black combination. There are other breeds too which come in varying shades of white and cream, such as the German Spitz.
Secondly, solid white is known to occur in breeds which definitely do not carry recessive black. Towards the bottom of the page we deal with white Schnauzers, and these are one example. Cream doesn't occur in this breed (although the white is often an ivory shade), so in some ways it provides a better example of solid white than the variable Samoyed does. Yet Schnauzers are known to carry dominant black, not recessive. There isn't even a chance that they carry "hidden" recessive black, because they only have the a^t and a^w genes on the A locus (a, which is recessive black, is also on the A locus).

So overall, although it seems to make sense that a recessive black/recessive red dog would be solid white, there's no evidence to suggest that this gene combination is in fact responsible for white. It seems much more likely that it's simply down to an extreme dilution of phaeomelanin (red) on a recessive red dog.

All of these dogs have tan points (a^ta^t) which have been affected by one of the chinchilla genes. The Canadian Eskimo Dog has the extreme white pattern (s^ws^w), which covers up most of its markings, but we can tell it has tan points because of the pattern on its cheek (which corresponds to the tan point pattern, as on the other dogs). This pattern is too regular to appear naturally in an extreme white piebald. The Finnish Lapphund is a liver-and-tan (bba^ta^t). The main colour on a tan pointed dog can be black, liver, blue or isabella, and this applies to tan-pointed dogs with the chinchilla gene too.

These Tervuerens show the effect of chinchilla on heavy sable. The dogs on the left and right have normal expression of red, and the dog in the middle has one of the chinchilla genes. Its red has been diluted to a washed out greyish cream, and its black is unaffected.

The Canadian Eskimo Dog here is a rare example of the effect of extreme phaeomelanin dilution (probably platinum, c^p) on what is most likely a shaded sable (a^ya^y) or a saddle pattern (a^sa^s). Only the dark eumelanin pigment on the back remains, and all of the red phaeomelanin pigment has been diluted to ivory (not pure white - the coat has a noticeable cream sheen). The eumelanin is liver-coloured because this dog is also bb on the B locus (look at the nose if you're unsure about the back - it's definitely liver!).

All of these dogs are examples of recessive reds (ee) and clear sables with one of the stronger chinchilla genes. Their colour varies from cream to white. Breeds with this combination of genes include Bichon Frise, Samoyed, American Eskimo, German Spitz, Maltese, Bolognese, Akita, Shiba Inu, Saluki, Anatolian Shepherd, Labrador, Komondor, Puli, and Pekingese, among others.

URAJIRO

Some breeds of dog, most notably the Japanese Akita Inu and Shiba Inu, display a pattern known as "urajiro". Urajiro appears as white points, usually on a red dog. The points are located in roughly the same places as on a tan-pointed (a^ta^t) dog, but of course, normal tan points don't appear on red dogs, only black, liver, blue and isabella.

No one knows which gene (or genes) causes urajiro, but it's possible that it is connected to the C series. One theory is that urajiro is in fact tan points diluted to white. For this to work, there must be a dilution gene which affects only the red found on tan points and not normal red. A red Shiba with urajiro would then be a recessive red with diluted tan points (which aren't usually visible because of the red body on a recessive red). However, red urajiro Shibas often show sabling (known as "sesame" in the breed), which wouldn't be possible on a recessive red dog. They must therefore have a^y on the A locus, meaning they can't have tan points, because tan points are also on the A locus.
A second, and more plausible, theory is that the gene causing urajiro is a completely unique one which restricts pigment to the warmest (upper) parts of the dog, leaving the limbs, underparts and other extremities white. Only red areas (phaeomelanin) are affected. This can be seen on black and tan Shibas - the urajiro does not advance any further than the edges of the tan markings, unlike on sesame (sable) Shibas, where it often goes further than the normal tan pattern. Urajiro also doesn't seem to affect black masks.

Black and tan Shiba Inu with urajiro (causing some of the tan to lighten to white).

Jersey here, belonging to princesstiffany from PCG, shows urajiro on a puppy and an adult. He also has a few white markings (on his chest, toes and trim), which are not urajiro. Notice how his black mask has not been affected by the urajiro.

Interestingly, Shiba Inu and Akitas also come in a whitish colour (seemingly the same as platinum). This may be more than just a coincidence, and could indicate that urajiro is actually caused by the same gene/s which normally cause phaemelanin dilution, except affected by some sort of modifier which restricts the dilution to certain areas. The cream/white dogs are simply those without the modifier. Alternatively, the solid cream may be caused by an entirely different gene, so cream/white dogs may also have urajiro, but it's just not visible because of the base colour.

The Chihuahua and Saluki above also show an urajiro-like pattern. At first glance it looks like they have irish spotting, but the white goes up the inside of the hind legs and forms pips above the eyes, just like in urajiro. This is evidence of a pigment-restricting phaeomelanin dilution gene in breeds other than the Shiba Inu and Akita. It may be the same gene as urajiro, or just a very similar one.

HUSKY COLOUR

Huskies and Alaskan Malamutes have a very unique coat pattern, which usually consists of grey and black hairs on the back and head and white on the underside. How is this formed?

There doesn't seem to be any sort of "official" explanation for the Husky pattern, but here is my own understanding of how it works. It appears that Huskies are dogs with the wolf grey/agouti pattern (a^wa^w on the A locus, and kk on the K locus to allow the A locus to be expressed). Usually this appears as a dark sable-type pattern, like on this "wild boar" Wire-haired Dachshund (photo taken by June, as well as the Keeshond and Elkhound below):

The dark hairs are confined to the top of the dog, with the paws and muzzle a definite red. When this pattern is combined with the chinchilla gene, the red paws and muzzle become cream and the undercoat lightens to produce a greyish look. This is the typical "wolf grey" pattern, and is seen on breeds such as the Keeshond:

Combined with the extreme chinchilla or platinum gene, all of the red in the coat is lightened to white, as in this Swedish Elkhound:

Notice how there are scattered white hairs and white banded hairs in the grey areas. These would be red in a normal agouti, but have been turned to white by the blanket dilution of phaeomelanin caused by chinchilla. The black hairs and black banded hairs have been left dark because chinchilla does not affect eumelanin.

Now, the Elkhound above seems to be very similar to a Husky, so we can conclude that the Husky colour also comes from the wolf grey pattern with chinchilla dilution of phaeomelanin. However, the pattern isn't actually identical. Let's compare the Elkhound with a grey Husky (picture taken by Kenzie):

The main difference between the two is that the white covers a much larger area of the Husky than the Elkhound. The Husky definitely has some white markings, because it has an obvious blaze on its head. However, the rest of the white seems to occur in a very regular, symmetrical pattern, which is almost exactly the same on every Husky. It seems too regular to be caused by normal white, and also occurs in areas you wouldn't expect to see white in the irish spotting pattern (such as around the eyes and on the underside of the tail). But what does this pattern remind you of? It actually looks very similar to the urajiro pattern above, although it extends further.

My personal belief, then, is that the Husky pattern results from the interaction of three genes - wolf grey, extreme chinchilla (or platinum), and some form of urajiro (whatever that gene actually is). However, this urajiro would have to be a different sort to the normal one, which only affects red. This one presumably affects black pigment too. Huskies and Malamutes with red hairs inamongst their black hairs are presumably wolf greys with urajiro but no chinchilla gene, so they don't have blanket dilution (i.e. they don't have dilution all over), only dilution of their "points". This would mean that urajiro and chinchilla are two entirely different genes, occurring on different locii.

One problem with this theory is it doesn't explain dogs like this:

The urajiro (or just diluted red points on a wolf grey? Could be either in this case) is obvious on this dog. He also has white hairs inamongst his black hairs, indicating that he has blanket phaeomelanin dilution (so chinchilla). But then, where do those traces of red on his legs come from? The chinchilla gene should have turned those areas to white. If he had urajiro but no chinchilla, there is no explanation for the white hairs in the black areas (they should be red).
I have no solution to this, unfortunately. The "three gene" theory seems to fit Huskies most of the time, but this dog has me stumped. If you have any ideas about this, feel free to contact me!

SCHNAUZERS

Schnauzers are a very interesting set of breeds, colour-wise. When researching dog genetics I had great difficulty finding anything which related Schnauzer colours back to general genetic theory, so I thought I'd have a go myself.

The Miniature Schnauzer comes in four colours - solid black, solid white, salt-and-pepper, and black-and-silver (in the traditional tan pattern). Salt-and-pepper is just like black-and-silver, but the black is replaced by grey. This is what makes the genetics of Schnauzers confusing - black-and-silver and salt-and-pepper look like they're caused by the same gene, but we don't know of any genes like this.

In fact, salt-and-pepper and black-and-silver are caused by different A locus genes combined with one of the chinchilla genes.

This salt-and-pepper Schnauzer (photo taken by June) has quite long fur, and gives an important clue as to which gene is really responsible for this colour. Some of its hairs have black tips. Tipped/banded hair is characteristic of agouti (a^w). Yep, this Schnauzer is wolf grey, like the Elkhound in the Husky section above. Many Schnauzers have very short fur due to stripping for the show ring, so often banding isn't visible.

This black-and-silver Schnauzer looks like it has the same pattern of white as the salt-and-pepper above. However, the white on this dog is caused by the tan point gene (a^t). Tan points are on the same locus as wolf grey, and produce a very similar sort of pattern, but the upper parts of the body are a solid colour with no banding.

All Schnauzers are homozygous for chinchilla (probably extreme chinchilla or platinum). This means that agoutis become wolf greys (salt-and-pepper) and black-and-tans become black-and-silvers. All of the phaeomelanin in the coat is affected, because Schnauzers don't carry any sort of urajiro like the Shibas above, even though they look a little bit like they do.
Solid black Schnauzers have the dominant black gene (K), which stops the agouti locus patterns from being expressed. A black Schnauzer is genetically a salt-and-pepper or a black-and-silver, but is unable to express either of these. A salt-and-pepper or black-and-silver dog must be kk on the K locus in order to express its pattern.
Solid white Schnauzers are genetically recessive reds (ee on the E locus). Recessive red turns all of their black hairs to red (recessive reds have a faulty mechanism which means they're unable to produce eumelanin, or black pigment), and then the chinchilla gene turns them to white, leaving their noses and eyes unaffected. White Schnauzers can be genetically black, salt-and-pepper or black-and-silver. The combination of recessive red with chinchilla is a fascinating one, because it's the only thing, except for white markings, which can hide any colour or pattern. There is nothing which can "override" it, because it stops the production of all eumelanin and dilutes all phaeomelanin, and these are the only pigments present in dog coats. All dogs with those two genes together will be solid white (or ivory), and it is impossible to tell which colour or pattern they actually are unless you know the family history or have access to genetic testing. Perhaps only a sad, obsessive person like myself would find that fascinating, but still!

Just to illustrate all this stuff about Schnauzers, here are some genotypes (taking into account only the locii that matter in this breed - A, K and E). I haven't included all the possible genotypes, just a few to give you the general idea:
a^wa^wKKEE - homozygous for wolf grey, black and normal extension. Will be black (genetically wolf grey).
a^ta^tKkee - homozygous for tan points and recessive red, heterozygous for black. Will be white (genetically black and black-and-silver).
a^wa^tkkEE - homozygous for non-black and normal extension, heterozygous for wolf grey and tan points. Will be salt-and-pepper (wolf grey is more dominant than tan points).
a^ta^tkkEE - homozygous for tan points, non-black and normal extension. Will be black-and-silver (this and a^ta^tkkEe are actually the only genotypes which will result in a black-and-silver, making it just about the most recessive Schnauzer colour).

ALBINO

True albino, which is a recessive gene on the C locus, is not thought to occur in dogs. Sometimes dogs do occur which are completely white with pink noses and blue eyes, but these are probably semi-albinos. Genetic testing has not shown them to have any mutations on the C locus though, so it's possible that their lack of pigment is actually caused by something other than albino.

"White" Dobermanns are not true albinos (they still have some pigment, it's just very diluted), but geneticists are unsure which gene causes both their phaeomelanin and eumelanin to lighten so much. All we know is that the white Dobermann gene is recessive, which makes it similar to true albino.

ALTERNATIVE THEORY

Now that you're familiar with the idea of the C locus diluting phaeomelanin (red), it's time to say that in fact, although this is a well known and apparently widely-accepted theory, genetic testing has failed to find any basis for it. The C locus is known to cause dilution in other animals, but dogs with supposed C locus dilution have been tested and have been found to have nothing out of the ordinary on this locus. Even white Dobermanns don't appear to have any C locus basis for their colour, yet these seem to be as close to albino as dogs generally get, and both their phaeomelanin and eumelanin pigment is diluted, which doesn't happen with the other genes we usually assign to the C locus. It seems if any gene is on the C locus, it should be the white Dobermann gene, but it's not.

There are no suggested alternatives for the location of the white Dobie gene, but one alternative theory for phaeomelanin dilution is that it is caused by another locus, I. The I locus determines the intensity of phaeomelanin, similar to how the B locus makes black less intense and turns it into liver, but on some sort of continuum. Rather than a dog being red or being cream (like a dog is black or liver), there are thousands of shades of red, gold, tan, cream and white which all seem to be caused by the I locus. Exactly how this can occur with a limited set of genes is unknown, but it probably involves a lot of what geneticists call "plus and minus modifiers", which tell the gene to code for more or less intense pigment.

But anyway, for now, as we don't know much about this hypothesized new locus, it's best to stick to the C locus theory, which works so long as we don't want to get too detailed or accurate. For our purposes anyway, it's OK. Just be aware that it is by no means certain, and is actually far more likely to be incorrect than correct.

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