• Home Contact Us What's New New Litters Puppy ExportsAbout Us Pom Reader Kennel Visit Poms in Canada Kennel Visit  • About Poms Stud Services Links Photo Album • 

   • Fun Photos New Damascusroad ChampionshipsPuppies Growing Up List of ArticlesAbout Pet FoodSkin/Coat Care Vaccination Information CKC Breed Standard • 



by Dr Leith Bungey  

"Genetics, whether of the dog or Homo sapiens, is never a simple subject that can be simply explained." (Onstott 1978;ix)  

Even a cursory examination of the substantial body of research reported in the literature would indicate, however, that the decision to not introduce the merle modifier into the chihuahua gene pool in Australia was a simple one.  That is, merle small dogs are not purebred chihuahuas, they are cross-breeds, mongrels, and cannot be registered with the state canine associations.   

The merle gene is in fact a modifying gene (Whitney 1971;192), that is, it genetically alters and lightens dark coloured coats as well as the pigment in the iris of the eye and the middle ear (Lambert 2004).   

GM chihuahuas!  While there is considerable uncertainty about the ramifications of genetically modifying foods, there is ample scientific evidence of the dire consequences of the merle gene in dogs. 


Whitney (1971;194) states that to his knowledge, there is no solid white in dogs.  Whites include the albino white, the dark-eyed white and the common white associated with spotting.  Whitney (ibid;204) continues "There is one other white which is definitely different from the others so far discussed.  It is found in Norwegian harriers and in collies, both rough and smooth, and in shetland sheepdogs.  This is a white of a semi-lethal nature.  When one of these is crossed with a black-and-tan or tricolour, a curious colour called 'merle' is produced.  This white, which almost invariably weakens the possessor, is a very undesirable character ..." 


Willis (1989;275) reports that the association of merle colouration and deafness is well established.  In the homozygous state, the M allele causes rough and smooth collies to be almost white and research has shown that such dogs are usually deaf and have eye defects.


Dr George Strain, Professor of Neuroscience Comparative Biomedical Sciences, Louisiana State University of Veterinary Medicine (2004) states that dogs with blue eyes are 50% more likely to be deaf than are dogs with brown or black eyes. 


In the dachshund breed, the M allele leads to dappling.  The Hanover Veterinary School has maintained a kennel of dapple dachshunds since 1971.  The eyes of eighteen were examined of which nine were MM, five Mm and four mm.  All the normal mm dogs were devoid of eye anomalies while all the MM animals had a series of eye defects.  These included the absence of the Tapetum lucidum, lack of retinal pigment, a rudimentary lens, microphthalmia, microcornea, microcoria and other more minor conditions.  Mm cases also had similar eye problems although less severe in most instances.  These researchers consider that breeding with the merle factor should be restricted to scientific purposes where it might be useful in examining depigmentary disorders in man such as the Klein-Waardenburg syndrome associated with eye and ear defects (Willis 1989;228/9). 


As well as identifying eye and ear problems, the Hanover research revealed impairment of sperm production in both MM and Mm dogs (ibid;275). 


Onstott (1978;237) found that "Merle to merle yields 50% of the progeny merle, 25% black and 25% white.  The whites will be both deaf and blind." 


Some breeders claim that as long as merle is not bred to merle, no genetic problems can occur.  
Willis, quoted above, is quite categorical, however, in stating that Mm cases DO suffer ear and eye defects similar to those in the merle to merle (MM) matings.  So where a dominant M is mated to a recessive m (Mm), which recessive we might not even know about, problems DO occur.  

A further complication is that Whitney (1971;139) found coat colour modifiers (such as merle) can be dominant but not show.  Willis (1989;70) agrees that some dogs may not even be identified as merles even though genetically they are.   

Thus, it is not possible to be absolutely certain that one is NOT breeding merle to merle.  


Lambert (2004) established that the rapidity with which merle chihuahuas appeared is highly unlikely to be due to a single mutation.  On ascertaining that the breeders of the first merle chihuahuas also had dachshunds, her group emailed those breeders.  They received not one response.  

Dr Strain (2004) confirms "It seems highly unlikely that a NEW spontaneous mutation in the recessive allele in your breed would produce the same phenotype of the dominant allele.  I could not say this as an absolute but in my opinion the merle has to have been introduced from another breed.  Because the merle pattern is dominant, it could not have lain 'silent' for many generations only to reappear fairly recently."  

Yes, the merle chihuahua has to be a cross-breed.  So in addition to the still-experienced pomeranian small erect-carried ears, slightly oval eyes, slightly flat skull and harsh coat, or papillon colouring, nose, eyes and butterfly ears, chihuahua breeders would have dachshund-like or sheltie-like features with which to contend.  Certainly, some of the small merle dogs appearing on various websites have decidedly dachshund-ish or sheltie-ish heads with long noses and almond shaped eyes.  

A local veterinarian has recently brought to my notice that a larger merle dog such as a dachshund, sheltie or Aussie shepherd crossed with the chihuahua will result in heavier bone.  He believes that this additional weight is highly likely to be detrimental to the stability of particularly patellae, but also other joints, in our breed.  

A further issue is the possible appearance of blue (light) eyes in dark coloured chihuahuas which is not permitted by the breed standard. 


Willis (1989;298) concludes that we can never totally eliminate defects.  The rarer an allele becomes, the more difficult it is to reduce it still further so that a breeder's very success early in his breeding programme makes progress harder and slower in later years.  

He further states "Very rare defects, like some lethals, will be hidden for years, may not even be known about, and then will come to the surface under an inbreeding progamme." (ibid;327)  

Even with the most judicious of breeding, most of us have witnessed the sudden and unwelcome appearance of defects and undesirable characteristics we thought we had eliminated - or, indeed, we didn't even know about.  

Do chihuahua breeders in Australia want to expand this pool of defects and undesirable characteristics by bringing in the merle modifier and its various inherent problems?   

Certainly, the Germans do not and have banned the merle chihuahua (Lambert 2004) while Italy has banned both the merle cardigan corgi and the merle collie.  

The opinion of the Hanover Veterinary School researchers that breeding with the merle factor should be restricted to scientific purposes has already been cited above.   

Harmer (1975;9) agrees "... it would be better for merle to be a disqualified colour in all breeds."   

Australian Chihuahua breeders can do no better than to heed Stockman's (1990;44) advice, "Dog breeding is a tremendous challenge and can be enormously rewarding as a hobby.  But there is no place for the irresponsible ... think before you mate ...".  


Harmer, Hilary "Dogs and How to Breed Them" John Gifford Ltd 1975

Lambert, Gloria "Merles" unpublished paper 2004

Onstott, Kyle revised by Philip Onstott "The New Art of Breeding Better Dogs" Howell Book House Inc. 1978

Stockman, Mike in Trevor Turner Ed. "Veterinary Notes for Dog Owners" Popular Dogs 1990

Strain G. in Gloria Lambert "Merles" unpublished paper 2004

Whitney, Leon F. "How To Breed Dogs" Howell Book House Inc. 1971

Willis, Malcolm B. "Genetics of the Dog" HF & G Witherby Ltd 1989 

Reproduced with permission from the original author Dr Leith Bungey.

Source: http://www.istnet.net.au/~wachiclub/MerleMongrels.htm


The Trouble With Merle
     By C.A. Sharp

A breeder waits anxiously by the whelping box as her prize bitch breaks off her panting. The bitch’s mottled black and silver flanks, distended by late pregnancy, tense with another contraction. A membrane-wrapped bundle slides out of the birth canal. The bitch goes to work, cleaning her newborn. As the sack comes off, the breeder winces.

Several hours later the bitch sleeps on her side. Nine squirming puppies nuzzle her belly.  The breeder sighs. Three of the puppies are mostly white. Each of them has inherited genes—one from each parent—which cause major defects.

Every breeder’s nightmare? Did she know this might happen ahead of time? How about the stud owner? If either or both of them knew, how could they allow it to happen?  Some European breeders once made a serious effort to ban exhibition of dogs carrying this defective gene. It is called merle.

Merle is the Australian Shepherd’s signature color. So much so that the uninformed often mistake non-merle Aussies for some other breed. I remember a prominent breeder of years gone by telling me of an animated discussion she had with a self-appointed expert she met in a local park where she was practicing obedience with her National Specialty winner. The man insisted her dog was a Border Collie.  Nothing she could say would convince him. Finally she agreed that he must be right so she could get on with her training session. Many Aussie owners have had similar experiences.

There is only one other breed—the Catahoula Leopard Dog—where merle is more common than in the Aussie. We like the color. It is distinctive and beautiful. Unfortunately, the gene that produces it can also cause serious problems for a dog that inherits two copies. Homozygous merles—those with two merle genes—almost always have defects in sight and hearing. This is the reason that all Aussie breed standards used since the early 1970s have discouraged or disqualified “excessive white.”

The definition of “excessive” is sometimes hotly debated.  In the past, fans of flashy trim tried successfully to adjust the breed standard to allow a little more, specifically on the ears. Others damn it as a blight on the breed.

The standards have discriminated against extreme amounts of white because this type of coloration is usually—though not always—associated with merle homozygosity. An animal can also have too much white because of genes at the “S” locus, which codes for greater or lesser white markings. [See “Color Clashes”] Since homozygous merles—also called double merles, white merles, excessive whites or lethal whites—may have defects and since most homozygous merle Aussies are predominantly white, the framers of the breed standards discriminated against the color in order to discourage people from breeding these dogs.

There is a very simple way to avoid producing homozygous merles.  Never breed two merles together. This is the option many breeders choose.  However, sometimes the stud most ideal for your merle bitch is also a merle. If that is the case, you must be willing to decide before you breed just what you will do in the very likely case that you get homozygous merle puppies.

While a blind, deaf dog can live a full happy life—I know because I had one—it is not always the case. My dog flourished because of her upbeat, outgoing temperament. But a vet I once worked for had so many negative experiences with them that she felt poor temperament was characteristic.  I have never seen anything that links temperament to color, but the sensory deprivation caused by the merle defects probably exacerbates any inherent temperament weakness the dog may have.  Whatever its temperament, a blind and/or deaf dog is a responsibility no ethical breeder should knowingly foist off on anybody, no matter how well meaning they might be.

Deafness in homozygous merles results from a lack of pigment in the inner ear.  Hearing loss can vary but many of these dogs are profoundly deaf. Lack of pigment (white hair, pink skin) is associated with deafness in a number of species of mammal, including man. Dogs that have white markings on or around the ears due to white trim genes may experience the same kind of deafness.

The eye defects have been well described in the veterinary literature both here and abroad. They are extremely variable. Some individuals have only minor vision loss, but most are more seriously affected. Merle homozygotes will have some combination of defective irises, persistent papillary membrane, cataracts, subluxated lenses, and/or retinal defects. Interestingly, the amount of white even in homozygous merles does not correlate to severity of defects. In a study of the embryonic origin of merle eye defects, Dr. Cynthia Cook,, of the University of California, San Francisco, observed that severity of defect and amount of pigment were not related.

Common knowledge tells us that to avoid merle problems, never breed two merles together. The problem with common knowledge is that it may get the big picture but it overlooks the details. Consider the following scenario. A breeder calls me with a problem. A puppy in his new litter is solid, except for this little bitty merle spot on its tail.  “What color is it?” he asks.

“Merle,” I reply.

“But I’m gonna dock the tail!”

“Sorry, it’s still merle.”

“I could just register it as black.”

“OK,” I say. “Then what happens when someone breeds this ‘black’ pup of yours to a merle and, whoops, there are eye defects and white puppies in the litter?”


I’ve had several conversations like this over the years.  People in Aussies refer to these dogs as “phantom merles.” The more correct term is a cryptic merle. Since it is possible for a merle to have only a tiny amount of blue, it is also possible, though highly unlikely, that a dog might have a merle gene but exhibit no merle spots at all. There is no way a breeder would know this had happened.

When a non-merle, bred to a merle, produces pups with excessive white, many people are suspicious that the non-merle might be cryptic.  More likely, it and probably the mate carry genes for too much white trim. But if eye problems typical of a homozygous merle are found in the excess white pups, the apparently non-merle parent could actually be a merle. An ophthalmologist experienced in viewing merles should be able to tell the difference between merle eye problems and other diseases. If you suspect a dog is a cryptic merle, breeding it to another non-merle will tell you.  If you get at least 6 pups and none of them are merle you have a 98%+ probability that the dog is not merle. If you get even one merle pup, it is and any future breedings should be done with its true, though hidden, color in mind.

Our fondness for merle is yet another reason why we should have our dogs eyes checked by an ophthalmologist. Sometimes a homozygous merle will have “normal” merle coloring. A friend of mine had one. “ET” had only a moderate amount of white trim: Stripe, chest, one leg and her feet. She was from the Woods line, known for little or no white and very deep pigmentation. ET was medium blue and therefore “light” in color for her breeding. . She also had eye defects typical of a homozygous merle.

Variation in merle pigmentation is extreme, going from the virtual solids cryptic merles to a mostly light-colored animal with a peppering of full pigment. The color of the “blue” areas may vary from pale silver to deep gunmetal blue. Red merles may be anywhere from a buff to the color of iron-rich earth. The dark areas should be liver but appear more orange on some dogs.

Areas of intermediate pigment, called dilution spots, occur on some dogs and are probably caused by modifying genes. Animals with dilution spots are more likely to throw puppies that have them than those which do not.

There is a gene that modifies the merle pattern called “tweed.”   It was identified and was first described in the Australian Shepherd. Tweed merle dogs have extremely varied merle pigmentation. A blue tweed dog will have black spots, charcoal spots, slate blue spots, light blue spots and even dark brown spots. Red tweeds also exist. The tweed patterns are often remarkably regular and the result can be stunning. However there is a hitch. It can also cause white spots in places you don’t want them.

Tweed gene is a dominant that expresses itself only in the presence of merle. Therefore, solid color dogs are not affected even if they have the gene. Interestingly, homozygous merles also do not exhibit tweed. The reason for this is unknown.

Merle is not a gene that behaves itself. A classic incomplete dominant gene will exhibit three distinct types—one each for the homozygous dominant, the heterozygote and the homozygous recessive.   If a homozygous merle is bred, it has nothing but merle genes to pass on, so its offspring from a non-merle should always be merle and its offspring from a heterozygote will be either “normal” merles or homozygotes.

However, there is documentation of homozygous merles producing non-merle offspring. My bitch was one of them. Homozygous Aussies that produced non-merle offspring were the subject of a scientific journal article. This has also been reported in Collies and Shetland Sheepdogs and indicates that there is something inherently unstable about the merle gene.

Like a sharp knife, merle has many virtues but it can also damage. Breeders of merle dogs should be aware of its negative potential. Breeders of Australian Shepherds, the majority of which are merle, must be doubly so. 

Copyright © 1996-2002 by the author. No reproduction of any kind without the author's express permission. C.A. Sharp is a Member of the ASCA DNA Committee.

First published in Double Helix Network News, Vol. IV No. 2, Spring 1996, Rev. 2002

Copyright © 2001 Australian Shepherd Club of America, Inc.

Source: http://www.aussielads.com/Trouble%20with%20Merle.htm for original article.

Merle Free Pomeranians

Below are some of the many reasons why responsible Pomeranian breeders will not knowingly breed Poms which carry the merle pattern gene:

Birth Defects

The merle gene is associated with a number of birth defects including:
Eye problems including being born without eyes,
Hearing problems including complete deafness or born without ears,
Skeletal deformities,
Behavior problems (perhaps caused by blindness/deafness),
Skin and coat problems including cancer,
Puppy deaths in utero,
Puppy deaths shortly after birth.
For an excellent explanantion of these merle linked problems see http://mysite.verizon.net/coatcloset/id23.html and http://www.genmarkag.com/download/Factsheet_Merle_Gene.pdf

Some of these birth defects are progressive. For example, puppies may start out with normal hearing and sight but one or both may deteriorate with age. So an apparently healthy puppy may slowly become a deaf and/or blind adult. Other defects may also appear with age and the coat color may continue to dilute as well. Anyone considering purchasing or breeding merles should also ask themselves what becomes of all the puppies that are born with obvious birth defects so cannot be sold - they are commonly referred to as "bucket puppies" because that is where they often end up - in a trash bucket.

Cryptic/Masked/Phantom Merles

For a simple explanation of the genetics that can produce cryptic merles (also called masked merles or phantom merles) see http://www.lethalwhites.com/genetics.html.

To determine whether or not a Pomeranian carries the merle gene, a DNA test is now available. This test is only available through GenMark at a cost of $95.00 - see http://www.genmarkag.com/home_companion.php. Because the merle gene can be carried by an apparently normal dog, those that want to avoid this cruel gene will now have to add the expense of merle DNA testing to the other health tests that they already perform. Even those that want to produce merle puppies will have to perform this test to ensure that they are not breeding two merle gene carriers to one another since you cannot always tell by a dog's appearance if it has merle in its genetics.

Spontaneous Mutation

Spontaneous mutation is an extremely rare event. So rare in fact, that the astronomical odds of a pattern gene mutation to merle in both the hundred plus year old Pomeranian breed and the ancient Chihuahua breed, at about the same time, makes any claim of this happening beyond belief.

Some Chihuahua breeders believe that merle Dachshunds were used to create merle Chihuahuas (see http://www.istnet.net.au/~wachiclub/MerleMongrels.htm and http://www.tanyastoys.com/drwillis.htm). Chihuahua breed standards around the world have recently been modified to either ban the registration of merle Chihuahuas or to at least disqualify them from the show ring. Even in Mexico, the country of origin for the Chihuahua breed, merle Chihuahuas may not be shown or registered. On October 6, 2007 69% of the Chihuahua Club of America's membership voted to disqualify (DQ) merles. Unfortunately, a Director of the AKC, who is not a Chihuahua breeder, used his official stationary to send a letter to CCA members on January 19, 2008 to dissuade them from voting to change their standard to DQ merle Chihuahuas. Per AKC requirements, a final vote was taken in April of 2008 to add a disqualification of merles to the standard and, incredibly, it failed. You can find the sad saga of Mr. Gladstone's unethical interference in the Chihuahua standard revision to DQ merles at http://www.thedogpress.com/ClubNews/CCA-Merle-AKC-BreedStandard-0801.htm.

Even if the merle pattern gene did spontaneously mutate into the Pomeranian breed, it still does not negate the cruelty of intentionally breeding something this harmful. If wolves spontaneously mutated to look like sheep, would you want one in your flock?

Not Pure-Bred

Historically, Pomeranians have never displayed the merle pattern. In the many books written on the breed in the last 100+ years, not one reference to a merle Pom can be found. The bible of coat color genetics in dogs, The Inheritance of Coat Color in Dogs by Clarence C. Little, Sc. D. (first published in 1957) does not list the merle gene as one of the genes found in Pomeranians. Reports are that merle Poms started to mysteriously appear in the 1980s, however they were still extremely rare at that time. As soon as the pet industry realized that they could charge higher prices for this exotic pattern, many Poms were bred specifically to produce merles for financial gain.

It is believed that one or more unscrupulous breeders intentionally crossed Pomeranians with Toy Australian Shepherds and/or other merled breeds and falsely registered the resulting puppies that most resembled Poms as pure-bred. DNA tests which have been carried out on merle and non-merle Pomeranians seem to support this theory. However more tests need to be conducted and more reliable tests are needed before these tests can be used as proof positive that merle Poms are not pure-bred. If true however, not only have these irresponsible and greedy breeders introduced the health hazards associated with the merle gene into the breed, they have also now introduced genetic problems that were previously unknown in Pomeranians but which are associated with the merled breeds used to produce merle Poms.

Breed Standard

United States of America:
The AKC standard for Pomeranians, which is written by the American Pomeranian Club, was composed before merle Pomeranians were generally known. In the paragraph describing the head it says "The eyes are dark, ..." meaning that blue, green or light eyes are not acceptable.

The paragraph dealing with color says:
"All colors, patterns, and variations there-of are allowed and must be judged on an equal basis. Patterns: Black and Tan - tan or rust sharply defined, appearing above each eye and on muzzle, throat, and forechest, on all legs and feet and below the tail. The richer the tan the more desirable; Brindle - the base color is gold, red, or orange-brindled with strong black cross stripes; Parti-color - is white with any other color distributed in patches with a white blaze preferred on the head. Classifications: The Open Classes at specialty shows may be divided by color as follows: Open Red, Orange, Cream, and Sable; Open Black, Brown, and Blue; Open Any Other Color, Pattern, or Variation."

Since the merle pattern is not included in the patterns described in the standard, it should be clear that it is not one of the patterns that were intended to be allowed. To read only the first sentence, and ignore the remainder of the paragraph is simply taking the meaning out of context.

The American Pomeranian Club set up a committee to look into the merle pattern. The recommendation of this committee is that the merle pattern should be disqualified in the AKC Pomeranian standard. The APC has recently set up a Standard Revision Committee.

Fédération Cynologique Internationale (FCI):
The FCI standard for Pomeranians (also known as Toy German Spitz or Zwergspitz in German speaking countries) is used by most European, Asian, Central American and South American countries. Merles not specifically mentioned, but obviously not permissable. See http://www.fci.be/uploaded_files/097gb98_en.doc

Merles are not permissable or recognized. See http://www.pcoc.net/ckc-breed-standard.htm

United Kingdom:
Merles not specifically mentioned, but obviously not permissable. See http://www.thekennelclub.org.uk/item/197

Source:   http://www.ringsurf.com/ring_browser.php?ring_id=MerleFreePoms

 • Home Contact Us What's New New Litters Puppy ExportsAbout Us Pom Reader Kennel Visit Poms in Canada Kennel Visit  • About Poms Stud Services Links Photo Album • 

   • Fun Photos New Damascusroad ChampionshipsPuppies Growing Up List of ArticlesAbout Pet FoodSkin/Coat Care Vaccination InformationCKC Breed Standard •