Shetland Sheepdog Coat Color DNA Study

This page was mounted on April 23, 2009 and was last updated on December 15, 2012 by Dayna Dreger, PhD. The linked pages in this series by Sheila Schmutz (sheila.schmutz@usask.ca) may have been updated more recently however.

Shetland Sheepdog Colors

Allowable colors in Shetland Sheepdogs (Shelties) include sable, black and tan, and solid black, each with varying amounts of white spotting. Merle can be present with any of the base colors, resulting in sable merle, blue merle, or bi-blue. Traditionally, white spotting occurs around the collar, on the chest, fore and hind legs, tail tip, and often a facial blaze. Though not preferred or accepted in many breed organizations, Shelties can also be predominantly white, often with a pigmented head and a few pigmented areas on the body, a coloration called Color Headed White.

E Locus (MC1R)

Three alleles are present at the E locus: E^M, E, and e. The E^M and E alleles allow for the expression of both phaeomelanin (red, yellow, tan) and eumelanin (black, brown, grey) pigments, while the e allele allows for the production of phaeomelanin only.

Only the E allele is present in Shelties. A genotype of E/E k^y/k^y allows for the expression of the various phenotypes associated with the A Locus (ASIP or Agouti). Since clear red (e/e) and melanistic masks (E^M) are not present in Shelties, it is reasonable to conclude that these alleles do not exist within the breed.

Agouti (ASIP)

Four alleles are present at the A locus: a^y > a^w > a^t > a. Three of these alleles (a^y, a^t, a) are present in the Sheltie breed.

When this webpage was first mounted in 2009, the mutations for a^y and a had been discovered. The mutation in the promoter region that causes the a^t allele was discovered and published in 2011.

• Dreger, D. L. and Schmutz, S. M. 2011. A SINE insertion causes the black-and-tan and saddle tan phenotypes in domestic dogs. Journal of Heredity 102:S11-S18.

	The ay allele produces the sable color in Shelties. Characterized by a predominantly red coat, often with some solid black or black tipped hairs spread throughout. Valerie to the left is ay/ay.
The at allele produces a black and tan phenotype, that when present with white markings in the Sheltie breed, is termed tri-color. The at allele is recessive to the ay allele, but dominant to the a allele. The black and tan markings always occur in a predictable pattern. The dog will be predominantly black with tan markings on the cheeks, over the eyes, on the lower legs, and under the tail. In the absence of white markings, tan points may also be present on the chest. Romeo to the right has been genotyped as at/a. He carries the allele that produces bi-black (recessive black), but since at is dominant to a he expresses the tri-color phenotype.
	The a allele produces a solid black coat color that is inherited recessively, as opposed to the dominant black phenotype present in many other breeds. Since the a allele is recessive to both the ay and at alleles, it must be present homozygously (a/a) in order to be expressed. Since Shelties more often than not have white markings, the phenotype associated with the a allele is termed bi-black.

There is a common belief that one can predict when a sable Sheltie carries an a^t or a allele, based solely on the amount of black present in the coat. These dogs are termed "tri-factored" (a^y/a^t) and "bi-factored" (a^y/a).

Can you pick the "tri-factored" (a^y/a^t) dog?

The correct answer is located at the bottom of this page

Merle (SILV)

Merle is a phenotype that causes dilution of eumelanin (black, brown, blue, grey) pigment in a random pattern. It often results in a patchy or splotchy appearance. The amount of hair that is diluted and the location of the deeply pigmented areas are highly variable. Merle can be applied "on top" of any of the base colors present in shelties.

Also common with the merle phenotype is multi-colored irises, being a combination of brown and blue, as demonstrated by Sketch (above). There is no indication that blue or multi-colored eyes result in dogs with decreased vision.

A tri-colored dog like Romeo (above left) with merle becomes a blue merle dog like Silver (above right). Notice that the black and tan markings on both dogs are located in the same areas, the only difference is that the eumelanin on Silver is diluted in random patches.

A bi-black dog like Paris (above left) with merle (a/a M/m) is termed bi-blue, like Sketch (above right). The black regions will be randomly diluted to blue, and as there are no tan points on a bi-black dog, there will be no tan present on a bi-blue dog.

Sable merle is difficult to distinguish as there is often minimal eumelanin present on a sable dog. It is often easier to distinguish sable merles at birth when the hair is shorter and appears somewhat darker. Ellie, pictured above, has been genotyped as a^y/a^t M/m, termed tri-factored sable merle. It is very difficult to see that she is merle at all, so may easily be misinterpreted as being sable, causing serious health defects if bred back to another merle dog.

Merle is inherited in a co-dominant fashion, with the m/m homozygote having deep pigmentation over the entire body, the M/m heterozygote having the random dilution of the merle pattern, and the M/M homozygote (termed Double Merle) being predominantly white, often with deafness or vision difficulties.

White Spotting (MITF)

The average Sheltie has a very predictable white spotting pattern: white on the chest, around the collar, on the legs, tail tip, and often a facial blaze, though the amount of white present in each of these areas is variable.

New data has pointed to a mutation in MITF that causes white spotting patterns in numerous dog breeds. This mutation does not describe all white spotting, though, and the normal spotting pattern present in Shelties and some other breeds (Border Collies, Corgis, etc.) does not seem to be affected by the mutation.

CJ (top left) and Indee (top right) both have very minimal white, without a whole collar and only small amounts of white on the paws and chest. Valerie (bottom left) and Aurora (bottom right) have much more white, with thick white collars and white markings far up their legs. All four dogs have the same genotype at the MITF mutation, S/S.

Variation at the MITF mutation in Shelties, rather than affecting the normal Irish markings, instead spreads white up the flank and stifle and onto the back. Dogs that are heterozygous for the MITF mutation (S/s^p) are often termed "white factored". Dogs that are homozygous for the MITF mutation (s^p/s^p) have significant amounts of white over their body, often with more white areas than pigmented areas. Within the Sheltie breed, this phenotype is called "color headed white".

Below is a collection of pictures of tri-colored Shelties. The dog on the right, Holly, does not have the MITF mutation (S/S). The white on her hind legs does not extend up to the stifle and the white on her stomach does not extend up the flanks. The middle dog, Pilgrim, has one copy of the MITF mutation (S/s^p). The white on his hind legs extends over the stifle, and if you were to lift his coat the white on his stomach extends part way up his flank. The dog on the right, Banner, has two copies of the MITF mutation (s^p/s^p) and has noticeably more white than the other two dogs.

Holly, Pilgrim, and Banner are all tri-colored dogs, the only difference between them is the amount of white spotting. Consider white spotting as a layer that is applied on top of the dog's base color. If Banner did not have all the white along his body, he would look like Romeo.

Also to be noted, the MITF mutation that causes the white-factored or color headed white phenotypes does not appear to affect white facial markings. Holly, who is MITF S/S, happens to have the most white on her face. Where Pilgrim (S/s^p) has no white on his face, and Banner (s^p/s^p) has only a small spot of white on the tip of his muzzle.

The amount of white present due to the MITF mutation is variable to an extent. Below are two more Shelties, Delainey on the left and Voodoo on the right, that have been genotyped as S/s^p to show the extent of white spotting possible when carrying the s^p allele.

S Locus Genotype	White Markings
S/S	collar, chest, legs, tail tip
S/sp	"White Factored" - collar, chest, legs, tail tip, stifle and/or flank and/or back
sp/sp	"Color Headed White" - white over most of the body with few pigmented areas

Answer to the Tri-Factored Quiz

All of the dogs are genotyped as a^y/a^y except for dog A, who is a^y/a^t.

Many breeds have their own set of anecdotes to help assess color in individual dogs. As we learn more about coat color genetics, we are able to support or disprove many of these "truths". While they may be helpful in predicting which color alleles a certain dog carries, these breed specific rules should not be assumed to be 100% accurate.

Links

Canine Color Genetics by Sue Ann Bowling

Back to Dog Coat Color Genetics Main Page by Sheila Schmutz