The Trouble With Merle
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
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
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
“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
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
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
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
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
http://www.aussielads.com/Trouble%20with%20Merle.htm for original
Merle Free Pomeranians
some of the many reasons why responsible Pomeranian breeders will not
knowingly breed Poms which carry the merle pattern gene:
The merle gene is associated with a number of birth defects
Eye problems including being born without eyes,
Hearing problems including complete deafness or born without ears,
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
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.
For a simple explanation of the genetics that can produce cryptic
merles (also called masked merles or phantom merles) see
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
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
Some Chihuahua breeders believe that merle Dachshunds were used to
create merle Chihuahuas (see
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
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?
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.
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
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
Merles are not permissable or recognized. See
Merles not specifically mentioned, but obviously not permissable.