SHELTIE-COLORS GENETICLYThe different colors we see in the Shetland Sheepdog are caused by a various number of genes which are from various series. Some of these genes are the same in every Sheltie, like “BB” which gives the dog a black nose, “CC”, “DD” en “gg” which stands for intense pigmentation and on the extension series we find "EE" which permit pigmentation all over the entire coat. All Shelties have also white markings on the tip of the tail, chest and legs. It is also allowed to have white on the head and in the neck. Sometimes we see brown or black spots on the legs. The “T”gene accounts for the ticking, so Shelties with clear white markings carry “t t”. 
There are two main colors in the Sheltie, yellow (sable) and black. Both colors we can find on the A series, “ay” gives sable and “at” tricolor or to be correct black and tan. The “ay” gene is dominant to “at”. The tricolor is mainly black with tan on the legs, muzzle, above the eyes and under the tail. Nowadays all Shelties have white too. That's why we call this colour tricolour.
When you mate a homozygous sable (“ay ay”) to a tricolor all the offspring will be heterozygous sable “ay at”. The color of these sables are generally darker then the homozygous sable. An other name for these color is mahogany or shaded sable. 
Beside the “ay” and “at” Shelties can carry the “a” gene which is recessive to the “at” and off course also to “ay”. Two of those genes will result in a black coat without tan, the black and white Sheltie. These dogs are always homozygous for the “a” gene.
The blue merle is actually a tricolor but on the M series these Shelties carries the dominant “M” gene. The “M” gene dilutes the base coat-color and makes is silver-gray or blue with black patches. The dog with the merle gene may have blue eyes. This can be one blue and one brown or even part blue and part brown in one eye. The not merled dogs carry “mm” and must have brown eyes.
The black and white Sheltie may also carry the merle factor. This merled black and white we call bi-blue and looks like a blue merle without tan.
Unfortunately the English standard is still calling this color blue merle even though they have different genes.
The sable-merle is a sable with the merle factor, the sable coat shows light brown patches. When a sable-merle pup matures most of the time you won't be able to see the difference between a normal sable and a sable-merle coat. This and the possibility of blue eyes, which is not allowed in sables makes most breeders decide not to mate a sable to a blue merle. When we mate two merles with each other we have a 25% chance to get a double merle (“MM”). The coat color will be diluted twice. Quite often these Shelties are almost white, but also could be defective in sight and/or hearing. So it's not recommended to mate merle to merle. 
Nowadays all Shelties have white markings. The “si” gene is responsible for this phenomenon. This “si”, which applies to Irish pattern, is recessive to “S” that gives a solid color coat. The “si” makes the pigmentation impossible on certain parts on the body and white is left in it's place.
Some Shelties have the recessive white factor “sp” instead of the “si”. Geneticist named this “sp” the piebald gene. When a dog is homozygous for the “sp” we see a coat with a lot of white of over the body and sometimes only the dogs head is colored. They gave this dog the name color-headed white.
Don't confuse this color-headed white with the double merle white dogs. These color-headed white Shetland Sheepdogs are healty dogs but according to the English standaard patches of white on the body are highly undesirable.
Sometimes a white factored Sheltie (“si sp”) has a white spot on his body, but in most cases you can't see the difference between a “si si” and “si sp”, although some have a white stripe up to the knee. There appear to be modifying factors involved on the S series. The majority of plus modifiers will result in more pigment (less white) while the minus modifiers enlarge the areas of white.
This explains why some Shelties have huge shawl collars and others have a small splash. So a dog who is homozygous for the Irish pattern (“si si”) and who has a majority of minus modifiers can have the same amount of white as a white factored dog (“si sp”) who carries a large number of plus modifiers.
I would like to end with my thoughts about the color black and tan. This color is now extinct in the Shetland Sheepdog and the only Shelties I've ever heard of are Tango of Houghton Hill and Starling. I'm not sure about the genetics of these bitches. To my knowledge there has never been any study of the black and tan in Shelties. The most logical explanation is that, beside the “at at” or “at a”, the dominant “S” gene was present. For the “S” will result in a full colored coat without white. But this means that one of the parents had to carry the “S” also. In the English Charts we can read that the sire of Tango of Houghton Hill was a tricolor and the dam a sable. The tricolor sire speaks for itself. Carried the mother the S gene? Was she without white. If so, where there also blue merle without white or solid black Shelties. Lerwick Freya was an almost solid black Sheltie, she had no tan and only a few white toes and a small white spot on her chest. Was she “a a S S” with a majority of minus genes or “a a si si” with more plus genes. I wonder if we ever find out, if there ever will be black and tan born. 
Sometimes we see some strange colours like this Sheltie born in one of my litters. He is out of my blue merle dam and a tricolour sire.
He has the merle-factor because he has a few dark spots and blue in his eyes. At birth he was a bit darker. Probably he carries the "d" gen
as this gen also dilute the coatcolour and he has to be homozygous. This dilution can happen to all colours. Perhaps we have to deal modifying factors also or perhaps there are more other genes involved....
Click on the picture if you want to see this Sheltie at an adult age.
Karin M. Vrieswijk-Zeijlemaker |
