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 aren’t a result of blue pigment, but rather, the lack of pigment in the eye’s iris. This lack of pigment 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 blue-eyed dogs, but each is a separate, unrelated case. For example, dogs with the merle coat pattern usually have blue or partially blue eyes. Merle manifests on a dog’s coat as a pattern 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 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 developing the eye’s shape and color and 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
When breeds like Australian Shepherds, Border Collies, Dachshunds, Great Danes, and Cardigan Welsh Corgis have merle coats, they’re more likely to have lighter eyes due to the same gene.
The dominant merle gene M, which causes merle or double-merle coat patterns, is more likely to 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 specific 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’re mm. In merle dogs, sometimes M is an incomplete dominant. In this case, 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 and blue eyes. Unfortunately, they’re 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 predominantly white with small patches of color, or no patches of color at all. This pattern is caused by one or two recessive alleles out of the several alleles possible at the S location, called the white spotting locus. Scientists don’t fully agree on the genetic research behind this. Still, generally, a dog with two copies of the most recessive allele (sw) at that S locus will be primarily white, possibly with some patches of color.
The association between having blue eyes and a mostly white coat seems to only occur in certain breeds, with mostly white dogs in some breeds, such as Whippets, being 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 subtly spotted fur pattern made up of 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 cause 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 occurs when a dog has two copies of a particular albino gene. Because of associated health problems, albino isn’t an approved color in any AKC standard.
These coat types often genetically connect to blue eyes in dogs. However, not all dogs need to 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. Researchers discovered this 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 consented to their dogs’ DNA being used in other studies. The owners provided information about their dogs’ eye colors, which researchers compared to each dog’s genome sequence.
The study’s focus was to test genetic differences between dogs with blue eyes and dogs with 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 from the one that causes blue eyes in humans or in most other dog breeds. 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 wasn’t detected in any of the Alaskan Malamutes who were tested.
The gene appears to act as dominant, with 53% of blue-eyed Siberians having just one copy of the mutant gene. However, it’s not always solely because of this. Many brown-eyed dogs also carried one copy of the mutant gene, which is probably 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 different 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 undiscovered but uncommon genetic influences on blue versus brown eyes in Siberian Huskies.
While many different coat types coexist with mutant blue-eyed genes, the gene that specifically causes 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.