If the eyes are the windows to the soul, then blue-eyed dogs must have souls that sparkle. Some people attribute the ice-blue eyes so often found in Siberian Huskies to some mythical or supernatural force, but in reality, they’re just due to genetics.
Nobody knows how the Siberian Husky acquired this mutated gene, how long blue eyes have been present in the breed, or if it gives them any advantage in the winter and snow. They may not serve any real function, aside from their captivating beauty.
Blue eyes are not a result of blue pigment, but rather, the lack of pigment in the iris of the eye. This causes light to be scattered through the same mechanism that causes the sky to be blue. Because of the lack of protective pigment, people with blue eyes may be more susceptible to damage caused by ultraviolet sun rays. However, no evidence exists for such eye color-related damage in dogs.
Merle Coats and Blue Eyes
Most dogs have brown to golden eyes. But what dog breeds have blue eyes? Blue eyes can be found in a few breeds, most notably the Siberian Husky, Alaskan Klee Kai, Dalmatian, and Australian Shepherd. When we talk about blue eyes in dogs, the color may range from light blue to almost white and may involve both eyes, one eye, or just parts of one or both eyes.
Several coat patterns are often associated with dogs with blue eyes, but each of these coat patterns is a separate, unrelated case. For example, dogs with the merle coat pattern often have blue or partially blue eyes. Merle manifests on a dog’s coat as a pattern made up of irregular blotches of fully pigmented fur, set against a lighter background area consisting of the same pigment, such as solid black on gray or solid brown on tan. Because the merle pattern can be associated with major health problems like deafness and blindness, it is not recommended to breed two merles together.
In early 2006, scientists found the genetic basis for merle. Because of this study, a DNA test for merle is now available, and breeders are urged to use it to avoid producing double-merles. Geneticists compare aspects of double-merles with signs present in humans with Waardenburg Syndrome 2, pointing out that both groups have a genetic disorder that hampers the growth of pigment cells. Besides affecting hair pigmentation, these pigment cells also play a role in the development of eye shape and color and of the nerve endings in the inner ear. When the pigment cells are absent, the results are often blue eyes and deafness.
Dominant and Recessive Merle Genes
The dominant merle gene M, which causes merle or double-merle coat patterns, is more likely to also cause blue eyes in dogs. Dogs with one, but especially two dominant copies of this gene are likely to have blue or at least partially blue eyes.
A dominant gene, like the dominant merle gene, means a dog only needs one copy of the two possible gene variants (alleles) at a particular place (a locus) on the chromosome responsible for a particular trait. If a dog has just one copy of the dominant M allele, along with one copy of the recessive m allele (Mm), their coat will be merle.
A recessive allele, m, requires two copies for a trait to appear. Non-merle dogs have two copies of the recessive allele, so they are mm. In merle dogs, sometimes M is an incomplete dominant, which means that a dog with one copy of M and one copy of m (Mm) will be a merle, but a dog with two copies of M (MM) will look different. These so-called “double-merles” usually have large areas of white fur, as well as blue eyes. Unfortunately, they are also often deaf or blind.
Extreme White Spotting and Blue Eyes
Another coat pattern associated with blue or partially blue eyes is called extreme white spotting. In this pattern, which is unrelated to merle, a dog’s coat is mostly white with small patches of color, or no patches of color at all. This is caused by one or two recessive alleles out of the several possible alleles possible at the S location, called the white spotting locus. Scientists do not fully agree on the genetic research behind this, but in general, a dog with two copies of the most recessive allele (sw) at that S locus will be mostly white, possibly with some patches of color. The association between blue eyes and being mostly white seems to only occur in certain breeds, with mostly white dogs in some breeds, such as Whippets, much more likely to have blue eyes than others.
Roan and Blue Eyes
Another unrelated pattern, roan, is also more likely to be associated with blue eyes. Roan is a pattern of subtly spotted fur that features dark hairs intermingled with white. It’s most notably seen in the Australian Cattle Dog, roan is also behind the genetics that make up the spotting in the Dalmatian. This association with roan may be the cause of blue eyes in Australian Cattle Dogs and possibly Dalmatians.
Albinism and Blue Eyes
Unrelated to the other patterns, albinism occurs in a few breeds, and albino dogs have pale blue eyes. It takes place when a dog has two copies of a particular albino gene. Because of associated health problems, albino is not an approved color in any AKC standard.
Despite these coat types that often genetically connect to blue eyes in dogs, not all dogs have these coat types in order to have blue eyes.
Blue-Eyed Genetics in the Siberian Husky
The cause of blue eyes in Siberian Huskies is distinct from these coat pattern associations. This was discovered in a 2018 study using data from more than 6,000 dogs.
The study was the first to use data supplied by dog owners who purchased DNA profiles of their dogs from a for-profit dog DNA company, and who consented for their dogs’ DNA to be used for other studies. The owners provided information about their dogs’ eye colors, which researchers compared to each dog’s whole genome sequence.
The focus of the study was to test genetic differences between dogs with blue eyes compared to brown eyes. They found this difference on chromosome 18 near a gene known as ALX4. This gene plays an important role in the development of the eye. The mutated gene, called DlogR, changes how ALX4 codes for depositing pigment in the eye as it develops. Siberians with blue eyes were very likely to have an extra, duplicated snippet of DNA inserted in this region.
This mutation, however, is different than the one that causes blue eyes in humans or in most other dog breeds. But aside from the Siberian Husky, the study also found the gene in the Alaskan Klee Kai (a breed derived from the Siberian Husky), in a few Australian Shepherds, and an Australian Cattle Dog. It was not detected in any of the Alaskan Malamutes who were tested.
Although the gene appears to act as dominant (53% of blue-eyed Siberians had just one copy of the mutant gene), it’s not always solely because of this. A large proportion of brown-eyed dogs also carried one copy of the mutant gene. This probably is related to genes at other locations: for example, dogs with the gene for a dark facial mask were much more likely to have brown eyes even with the DlogR mutation.
Despite this, the presence of the mutant blue-eyed gene explained that the majority (82 out of 108 blue-eyed dogs, or 75%) of blue-eyed Siberian Huskies in the study. It made no difference whether the eyes were both blue, just one was blue, or just parts of one or both eyes were blue.
Same Genes, Brown Eyes
A large proportion of brown-eyed dogs carried one copy of the variant. Why didn’t they have blue eyes? Nobody knows. It may be related to genes at other locations in the dog. Sometimes genes can interact with, or even mask, the effects of other genes at unrelated locations. In this case, dogs with the gene causing a dark facial mask were much more likely to have brown eyes, even if they had the “blue-eyed” mutation. Why?
Somehow having a dark mask, or the gene for a dark mask, seems to cause pigment to develop in the eye, despite the blue-eyed gene calling for blue eyes. But it still isn’t that simple, since a few of the brown-eyed dogs didn’t have the dark-mask gene. This suggests there may be as-yet undiscovered but uncommon genetic influences on blue versus brown eyes in Siberian Huskies.
While there are many different coat types that coexist with mutant blue-eyed genes, the gene that specifically makes for blue eyes in Siberian Huskies remains a mystery. It’s not the same as what causes blue-eyes in other breeds, and can’t be attributed to the same genes that create these coat types either.