Identifying Double-Merles


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.


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.


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


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


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


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.


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.


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.


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.


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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14 Responses to Identifying Double-Merles

  1. Gina February 15, 2012 at 8:54 pm #

    This is totally off topic, but I clicked on the link “game mechanics and animal fancies” and saw your mention of the game Mille Bornes-I have to say THANK YOU! I remember this game from when I was about five, but could only vaguely remember what a few of the cards looked like and couldnt remember the name or how it was played, etc. I have been wondering forever what that game was! Sorry for the off topic post, but again thanks-this has been bugging me forever! (Love this blog/site by the way!)

    • The Equine Tapestry February 15, 2012 at 9:07 pm #

      I am glad you have enjoyed the blog, and glad the game name was helpful. I would happily send you our copy, if you need one! (If I can find that Right of Way card, that is…)

  2. Mary Jo Nerly February 15, 2012 at 9:07 pm #

    I had a blue merle Australian Shepherd that a all white head and very, very little color on the body. The eyes looked normal, but she was blind with no eye structure behind the eye. When you called her she would run into circles until she found you. It was so sad when she hit her head on the manure cart and cried and cried until I was able to console her.

  3. Kristina Pry February 15, 2012 at 9:13 pm #

    The AKC may not have any rules against it, but responsible breeders DO. My Sheltie is a blue merle and I would NEVER mate him against another merle. Ever. Not for any amount of money or how good the cross is.

    That being said, he IS white factored – crossed with a color-headed white or another white-factored bitch, he could produce color headed white puppies. But THOSE dogs ARE penalized in the AKC show ring, despite the fact the gene has been present in Shelties from their inception. Color headed whites come with no corresponding deformities, unlike the hearing loss you see in Border Collies.

    And yet this natural coloring is penalized so heavily in the ring as to essentially disqualify a dog with more than 50% body white. Tell me how that makes any sense at all – to disqualify CHW’s but allow double merles?

    • The Equine Tapestry February 17, 2012 at 6:36 am #

      The Collie I had as a child was white-factored, and my grandfather and his family had color headed white Collies. I wish the color was accepted in the Sheltie breed, because you are right – it has no connection with hearing loss.

      • countrymae February 26, 2012 at 7:53 pm #

        Surely you are kidding? White factored is quite old term for SINE/MITF. There are double dilute collies just check out Border Wars Blog and read how and who can help you with double merle breedings., and show your lethal double merle Shetland Sheepdog. Get the vacccination first now available for Giardia.

    • Allison March 24, 2014 at 1:16 pm #

      I am assuming that AKC allows single merle dogs/bitches to show because they usually have enough color to qualify (whereas a double merle will never have enough color to qualify).

      I think the contemporary color factor is ridiculous–I miss the days when there were only sables/goldens with well-proportioned eyes. Continuously attempting to construct the breeds with unusual or “unique” coloring and insistence on beady little almond-shaped eyes with mismatched irises (resulting in blindness or impaired sight) has not benefitted the breed, but brought the collies to a screeching halt.

      NO true shepherd in the Shetland Isles would consider the shelties that currently win in the conformation ring potential candidates for true working dogs.

      • equinetapestry March 25, 2014 at 6:40 pm #

        I need to do a follow-up post about the eye issues in Collies. Since doing some of the posts about merle, someone provided more information about microphthalmia and CEA in Rough Collies. It is sad to see what has happened to my favorite breed, though, so I find posting about it depressing!

  4. ellenspn February 15, 2012 at 9:17 pm #

    As the owner of a dog who was a double merle and had the eye issues, but not the deafness I thank you for pointing out the eyes. There are many more double merle breedings than need be in the world. I curse the people who bred my Roo for creating a dog with a strong work ethic, as most aussies are, who was also handicapped. I lost him a couple years ago to that scourge of a cancer called hemangiosarcoma right as he was starting K9 Nosework, which would have been the perfect sport for him.

  5. Sandy Tomezik February 15, 2012 at 9:54 pm #

    This problem also occurs in homozygous dapple (merle) dachshunds. My red double dapple girl was totally deaf, but, had normal vision. I have seen other double dapples with microopthalmia, with and without accompanying deafness. However, in dachshunds there is also “piebald”, which looks similar, but does not come with the health problems. As pretty as my Lacey was, I wish, now that we know of the health problems, that people would stop breeding double dapples.

    • The Equine Tapestry February 17, 2012 at 6:39 am #

      I think there is more awareness with Dachshund breeders now than there used to be. It also seems that the breeds like Dachshunds and Catahoulas, where merle isn’t so often paired up with the white patterning genes, have less extreme issues with their double merles. They are still damaged, but it seems like the severity isn’t as bad in many of them. But that’s just my observation from a relatively small set of examples. It would be interesting to see what a formal study would show.

      • countrymae February 26, 2012 at 8:04 pm #

        Well formal studies have been here. Well Dachshunds, Catahoulas, Border Collies, Great Danes, Collies, Shetland Sheepdogs …hey they are only a variety not a separate species. A merle is a merle and ” eye ocular problems in these breeds relating to merle gene is across the board in every variety of canine. Yes even the Catahoulas who can be blind and deaf. Catahoulas phenotype of merle expression may not make them white, but the health issues are there for lethal double dilutes genetically.
        Formal studies again have been done and results are in print. This does remain a work in progress due to the obvious affects of the complex genetic fallout of playing with a lethal gene.

      • The Equine Tapestry February 27, 2012 at 6:10 am #

        Yes, merle is merle across all breeds. What is not known is the other factors that might contribute to the problems, including other patterning genes. Just how the different mutations interact is not fully understood – both in dogs and in horses. Merle tends to come up on this blog a fair bit because it is like horse patterns in that regard; it interacts with at least one identified mutation (harlequin), and may do so with others. The fact that breeds that carry the white spotting patterns seem (in my personal observation) to have more dramatic eye damage than those that do not is interesting to me because that interaction is the part we don’t yet know well. It is something that, in my opinion, merits further study. If merling and white patterning combine in a way that amplifies problems, that is information breeders need to have to make good choices.

        I would also add that homozygous merle is not truly lethal. Damaging, yes, but not lethal. That distinction is important since horses have a truly lethal gene which shares a name with the slang term (“lethal white”) for homozygous merle. It is also a distinction many who rescue homozygous merles want to emphasize, since the dogs are viable and can be homed.

  6. Cindy Dalton June 17, 2012 at 11:37 pm #

    This dog seems to be a double merle…