Tag Archives | eye color

Albino Shih Tzu

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This is Angel, the Shih Tzu with the mystery color mentioned in my previous post. When my friend Gretchen contacted me, she wondered if Angel might be a pale lilac dilute. That is a dog that has both the blue dilution (dd) and brown (bb). The palest shades of lilac are usually the lightest color, aside from white, that most dog owners are likely to see. Angel’s skin is not a muted brown, though, but a clear pink – quite a bit lighter than would be expected in a lilac dog.

Although lilac dogs have the palest overall tone, when it comes to skin coloring the lightest colors can often be found in recessive red dogs that are also homozygous for brown (ee and bb). In Labradors, this combination is sometimes called Dudley. As this comparison image shows, Angel’s nose color (left) is considerably lighter than the one on the Dudley Labrador (right).

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The pink skin was consistent on the pads of her paws as well. This extreme absence of skin pigmentation is particularly striking to anyone accustomed to looking at dogs. As I mentioned in the previous post, dogs do not have pink skin under their white markings in the same what that a horse will. Unlike horses, white markings that cover the nose do not give a dog a pink nose. Dogs seem very inclined to retain at least some pigment in their skin, which is what makes a truly pink-skinned dog stand out.

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Pink Angel toes!

Historically, dogs like Angel have been called albinos. That is true even though most have blue, green or even hazel eyes. They also have traces of color in their fur, making it possible to discern hints of things like black-and-tan patterns, black masks or white markings. To someone immersed in the world of horse color, that would sound like a mistake. It is an article of faith in the horse color community that albinos must be white with pink or red eyes. Yet albino is the term used not only by owners and breeders, but in scientific literature. Researchers have told me that albino is a term that can be used strictly or more loosely. That is one reason why it is so very difficult to get a definitive answer to the question, “Can a true albino have blue eyes instead of pink?” It really does depend on who you ask!

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Angel has hazel-colored eyes, but would still be called an albino dog

I had first become aware of dogs like Angel when I stumbled across a paper on albino Pekingese when doing research on the Hanoverian Creams. I was also aware of a handful of of other more modern cases, mostly among the smaller Asian breeds. What I did not realize until I began looking was that while still quite rare, this type of coloring is more widely distributed among the different breeds (and even among what are probably pariah dogs) than I had originally assumed.

The timing of this could not have been better, too, because at least one type of albinism (or extreme dilution, if you prefer) in dogs was identified in just the last few months. The particulars of that mutation will be especially interesting to horse color researchers, but it merits a separate post. In the meantime, I have set up a new Pinterest board with a wide range of images of albino dogs. I tried to pick ones that showed the range of color in the eyes and the fur. As with the other Pinterest boards, I have tried to be sure to link the pins back to their original site to preserve the photographic credits. In the case of some of these pins, following those links will take you to further information and more photos.

And just a final note. Angel is in the care of the Crossroads Shih Tzu Rescue in Tallahassee, Florida, and is looking for her forever home. You can find more information on her Petfinder page.

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Identifying Double-Merles

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With all the controversy surrounding the double-merle sire of the Westminster Best in Breed Collie, I thought it might be timely to finally get this post up about homozygous merles.

The motivation for posting this was a Great Dane I encountered at a dog fair this past fall. The dog was a homozygous merle, but one of the attendees was unaware because she believed that double-merles were “all white or nearly all white.” The dog at the top of this post is a good example of what people expect when someone says double-merle. That is often what they look like, especially in breeds that also have white patterning in addition to the merle.

This was the dog at the dog fair.

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The speaker did not believe he was a homozygous merle because he had more colored areas than white areas. She insisted that he was just a merle dog “marked with white.” She was unaware that some homozygous merles actually have a fair bit of coloring on them. In my experience, breeds that have solid merles (that is, merles without any white patterning) tend to produce homozygous merles with more color.

A close look at the placement of the white on this dog will show why it comes from a doubling up of the merle, rather than a white pattern. Here I’ve filled in his merled areas so that he looks like a black dog with white patterning.

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Here are some white patterned dogs to compare, starting with a Shetland Sheepdog. He has the irish spotting commonly seen in herding breeds.

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Here is a very similar kind of white spotting found in Boxers. (This was the pattern discussed indirectly in this post.)

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And here is an Ibizan Hound with the pattern sometimes called extreme piebald.

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Even though the edges on the last example are more ragged and irregular, it still looks quite different from the tinted image of the merle Dane. The placement of the color is wrong for any of these patterns. Here is what it does resemble.

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These two patterns look much the same. That is because the only real difference is that the dog above has white areas where the Harlequin gene came and stripped the gray coloring away, leaving those areas white. The dog below (whose patches are actually gray) had this color stripped away by a second dose of merling. The white areas on both dogs have an outline and placement consistent with merle, not white patterning.

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The white areas on this Dane do not make sense for any of the common white patterns found in dogs. Look at the difference between his two front legs, where one is white well up to the body and one is dark down to the end of his foot. His hind legs are similarly patched and uneven, just as might be expected with a merle, but not with an irish or piebald dog.

The other giveaway are his eyes. Mixed colors can make it hard to assess eyes, but the problems with his eyes can be seen despite their coloring. This first photo shows how the black pupil of the right eye has “bled” down into the lower part of the eye. This is common among homozygous merles. His left eye, meanwhile has an unusually small pupil, which is why the eye appears so very blue in this picture.

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If you look carefully at that first eye picture, you might notice an odd angle to his eye. I suspect from this shot, it is something more likely to jump out at those of us who sculpt animals. These next pictures show it more clearly.

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If the nature of his pattern was not enough of a clue that he was a double-merle, his eyes would give him away. Defects like this are typical.

This is also one of the reasons why the production of homozygous merles tends to generate some very emotional reactions. This particular dog has eyes that certainly look “wrong”, but his appearance – as double-merles go – is actually pretty mild. The eye deformities in many other homozygous merles are quite frankly disturbing to see. It is not just that homozygous merles are often blind and deaf, but that fact that hey look maimed is particularly upsetting. This probably contributed to rules in many countries that merle to merle breeding is abusive and therefor not permitted. Unfortunately, in the United States the Rough Collie registry has no such rule.

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Results are starting to come in on the Splash tests

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Some of the first test results from the new Splash White tests have started trickling in, and they are proving really interesting. I hope to update the Splash Project page over the weekend, but here is some of what we have learned so far.

As far as I am aware, those horses that have tested positive have all had the SW1 gene. That means the exact nature of the other two versions (SW2 and SW3) is still a mystery.

So far, with really limited results, it does look like in identifying SW1 researchers may have found the gene responsible for Classic Splash. That was the pattern originally described by Klemola in the 1930s. Even more exciting is that the one horse known to have tested as homozygous does have the classic pattern. That horse can be seen at the bottom of the first post on this forum.

Another interesting horse in that group is the homozgyous tobiano. There had been rumors that the KIT gene had been ruled out as a location for Splash White. I had explained why the KIT location was important in limiting the number of color mutations in this previous post, “Location Matters.” If the general rule that was explained there – that a horse should only have two mutations on any given gene – holds true, then finding a horse carrying two KIT mutations and splash white should tells us that splash white is not on KIT. The two tobiano genes would already take the two KIT slots. It is my understanding that there have been at least two horses tested as homozygous for tobiano that also have the Splash White gene.

That opens the door to the idea that there may be a lot more tobianos out there carrying SW1 than we might have previously expected, because  it isn’t an either/or situation. A horse could carry and pass along both patterns. What is also interesting is that tobiano has a way it sometimes skews that creates a dark patch with an odd “point” that drops from the croup. Some of us have long wondered if that might come from Splash, and now a horse with that kind of pattern has tested to be a carrier. It will be interesting to see if more horses with that kind of “point” also test positive, especially those that do not have such splash-like facial markings.

The other big news out of the early results is that there are horses that are coming back with blue eyes that test negative for all three of the Splash genes. It is really too early to know exactly what that means. Obviously more things cause blue eyes than just Classic Splash because they found those two other genes. It may be that there are still more versions, or it may be that one of the many yet-to-be-identified sabino patterns are involved. What we can say is that blue eyes are not caused by just one or two things. The situation is more complex than that. But then if pinto tests have told us anything, it is that it is all more complex than anyone originally thought!

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