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Color Genetics in English Bulldogs

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UC Davis now offers the MERLE Test! https://www.vgl.ucdavis.edu/services/dog/Merle.php
So many people want to swear that English Bulldog breeders are mix breeding & hanging papers to get Merle Bulldogs. Most believe whatever they are told, or what they read without any backing to prove the belief, yet they still believe it & will actually accuse others of wrongdoing without any facts to back up the accusation.

That is pretty sad since there are many VERY reputable breeders that have a conscience & ethics....so I have compiled some info here, that can be backed up with science, and by Professionals with the education to state what is correct.

We are not so misinformed, though that we do not realize that there are breeders who HAVE cheated, mixed, and hung AKC papers taking shortcuts to get the Merle in their program. This makes it even harder for the ethical breeder of Purebred AKC Merle English Bulldogs.

As for our breeding program, we have parentage DNA with AKC on all our dogs associated with our Merle Program. Our Merles are PUREBRED AKC Bulldogs (English Bulldogs). AKC themselves list ALL Breeds in connection with the Merle pattern as do others as you will see below.
More info on merles:   The Official Rare Color Chart  Marvelous Merles   8 AKC Generations of Merle
This page is not just my opinion. Every word on this page has been taken from articles of Scientists, Geneticists, Doctors, etc. all of which can be found by the links at the bottom of this page. It took me 5 months to read & go through all the websites & articles and excerpt the pertinent info that applies here.
Merle can be hidden by other genes,  and patterns, sometimes for long periods of time. This is why the merle gene can & has ALWAYS been in EVERY breed and is backed up by scientific fact.

Hidden merles are merle dogs who do not exhibit the merle pattern because their coat color does not show the pattern. Merling is not normally shown in red, gold, fawn and cream coat colors.  The hidden merle can be distinguished only by a genetic test.

1. Recessive Red

Merle can be completely hidden by recessive red, as recessive red dogs can't make eumelanin pigment and merle only affects eumelanin. A recessive red merle is known as a phantom merle.

2. Sable

A clear sable (dog with a red coat, but no visible black sabling) will also not show any merling because there is no eumelanin to be merled, unless it also has a mask (which does show merling). 

Shaded sables will often show merle at birth, but it tends to fade as the dog grows up, so all that remains on an adult is usually a few darker brownish patches on the coat (which can be hidden very easily by thick or long fur).

3. The greying gene can also make it very difficult to see merle markings.

4. The dilution gene (dd), because it dilutes the patches to roughly the same color as the base.

5. Brindle

Merle can be very difficult to see on a brindle too, due to the stripes.

6. Heavy Markings

Merle can be hidden if the dog has very heavy markings, so a black merle could appear completely black if the patches are large enough (a cryptic merle).  

Partial Excerpt from the UCDavis Website

Merle is an incompletely dominant coat color pattern characterized by irregularly shaped patches of diluted pigment and solid color. Breeds with merle include but are not limited to: Shetland Sheepdog, Collie, Border Collie, Australian Shepherd, Cardigan Welsh Corgi, Catahoula Leopard Dog, Dachshund, Great Dane, Bergamasco Sheepdog and Pyrenean Shepherd.

Merle only dilutes eumelanin (black) pigment; dogs with an MC1R ee genotype (recessive red) have no black pigment, thus do not express merle but can produce merle offspring. There are 3 alleles (variants) for merle: merle (M allele, SINE with longer poly-A tail), cryptic merle (Mc allele, SINE with shorter poly-A tail) and non-merle (N allele, no SINE insertion).

Dogs with cryptic merle (also called phantom or ghost merle), typically display little to no merling and some may be misclassified as non-merles.

Inheritance of merle is genetically unstable for both M and Mc alleles. During DNA replication and cell division, M may occasionally undergo poly-A tail reduction to produce Mc (germline rate of 3-4%) while Mc may undergo expansion and revert to M. Because of the complexities of merle inheritance, and potential health concerns, DNA testing is recommended to establish the genetic make-up of dogs for the merle gene for those breeds where this color dilution pattern is present.

The Veterinary Genetics Laboratory is licensed to offer the merle test.

Results are reported as:

M/M 2 copies of merle are present (double merle)
M/Mc 1 copy of merle and 1 copy of cryptic merle are present
M/N 1 copy of merle is present
Mc/Mc 2 copies of cryptic merle are present
Mc/N 1 copy of cryptic merle is present
N/N No copies of merle or cryptic merle are present


Clark LA, Wahl JM, Rees CA, Murphy KE. Retrotransposon insertion in SILV is responsible for merle patterning of the domestic dog. Proc Natl Acad Sci U S A. 103(5):1376-1381 (2006).

Kaelin CB, Barsh GS. Genetics of pigmentation in dogs and cats. Annu. Rev. Anim. Biosci. 1:16.1-16.32 (2013).

Screenshots of TOP Scientific Labs, Registries & Universities that include MERLE in ALL BREEDS of Dog.


Quotes from Doctors & Scientists

In talking to breeders and doing additional research, it is apparent that this color pattern is not new. Up to recent time a dog with the merle color pattern was described as spotted, mottled, incorrectly as brindle, and in some incidences not addressed in the color description of the dog at all.

Clemson University Canine Genetics Research Laboratory

Dr. Leigh Anne Clark and her team, who mapped and sequenced the merle gene in 2005, tell us that it is the same gene in all breeds. She and her fellow genetic researchers draw the conclusion that “the breeds analyzed in this study (the mapping /sequencing study) share a common ancestor,” and that “the occurrence of merle in many breeds . . . suggest that the founding mutation may predate the divergence of breeds.”

Revising Breed Standards

I believe the standard of any breed should undergo revision when genetic information and science dictate.

Articles published in scientific journals in recent years have added new information to our understanding of the merle gene. Why would we close our eyes to this new educational opportunity? Why not apply what we know now? 

“Those who say we should not be accommodating the Standard to what we are breeding, or that our present Standard was outlined by our founding fathers, need to review all the Standard changes since the mid 1800’s . . . I would like to think that we make changes in the Standard to clarify certain areas for breeders and judges as well as to correct errors as we gain more knowledge, especially in areas of genetics and inheritance.” 


Merle Breeding Help

The M locus is the home of the merle allele. Merle is dominant, and so denoted by the capital letter M. Non-merle is recessive, and denoted by m.

Merle is interesting because all normal merles are heterozygous (Mm). A homozygous merle is actually a double merle.

Merle affects only eumelanin. That means that any black, liver, blue or lilac in the coat, eyes or nose will be merled, whether it's the whole of the body, a mask on a sable, shading, brindle stripes, or even a saddle. Phaeomelanin (red) is not affected at all and will appear as normal.

Most Black based Merle dogs are called "blue merles" because of the bluish color between the patches in their coat. This is a widely-used term but is actually misleading. Technically they should be "black merles". Their nose pigment is black and their eyes are brown or blue. They are able to make normal eumelanin in their coat, so their patches are black. If they didn't have the merle gene, they would be solid black. "Blue merle" is misleading because it seems to say that these dogs have blue pigment (dd acting on black), when in fact they have black.

The random coat dilution caused by merle also affects the eyes and nose. The eyes may be all or partly blue, and the nose may be all or partly pink. Not all merles have blue eyes or pink noses though, and merles with heavy dark patching are more likely to have normal eye and nose pigment.

Due to the unstable and variable nature of the merle gene, sometimes merles have patches that are only partially diluted, and are between the base and the patch color. These are known as dilute spots, and they may sometimes appear brownish. Dogs with very extensive dilute and/or brown patching are likely to be tweed merles.

We talk about coat color being "diluted" in a merle, but note that dilute spots don't have anything at all to do with the Dilution gene (d), and are just a normal variation of the merle pattern.

Merle acts on the black pigment in the iris of the eye just as it does on the coat, so merle dogs often have part or all of the eye blue. (This does not affect their vision, though since it happens to some extent in the retina as well it may make it harder to diagnose certain eye problems.)

There are always two copies of a gene, alike or different, in any dog. If we call the merle gene M and the non-merle gene m, any given dog can be mm, Mm or MM. The mm dog is the normal.  The Mm dog is a blue merle, chocolate merle, lilac merle, black merle, or sable merle, depending on what color it would have been without the merling gene. An MM dog, often called a double merle or a homozygous merle, will be mostly white and sometimes can be associated with deafness or blindness.

Breeding merle to full color will produce one half full color and one half merles, but no defective whites. The merle to full color breeding, then, produces just as many merles as does the merle to merle breeding, and without the danger of defective puppies. The safe breeding for a merle, then, is to a non-merle mate. This breeding should produce all healthy puppies, and about half will be merles.

Sable merles are no more likely to have health problems than any other color.  The real argument against sable merles is that they may be mistaken for normal sables. If two such sable merles were mated together, the resulting litter could contain defective whites. What a shock for the breeder that may produce lethal whites.

Very few breeders have been lucky enough to get high quality homozygous (double) merles that are not too severely affected to breed - but it definitely takes a lot of luck and really top quality black merles to start with. Merle to merle breedings are only for the very experienced breeder who knows his/her lines and what they will produce, and it has probably produced more heartbreaks than good homozygous merles, even for the experienced breeder.

There is no such thing as a sable, blue, chocolate, lilac, or black merle gene. There is only a merle gene. Merle is a dilution gene, that is, it lightens whatever the coat color would otherwise have been. The lightening is not spread evenly over the coat, but leaves patches of undiluted color scattered over the dog's body. Also, the lightening seems to work primarily on the black pigment in the coat, so any tan on the face stays even.

Cryptic merle

Cryptic merle (phantom merle) are dogs that show only very slight merle coloration and in some cases it is not visible at all. The dog can have only small patches of merle, for example, at the end of tail or ear or the merle coloration can be concealed by white markings.

These dogs carry the shorter version of the merle gene, sometimes one copy and sometimes two copies. Unlike regular merle dogs, in the cryptic merle dogs no serious health problems connected with the regular (not shortened) merle allele have been described. They apparently have no eye or hearing problems. Dogs with two copies of cryptic merle gene (Mc/Mc genotype) or dogs with one cryptic merle copy and one regular merle copy (M/Mc genotype) have no health problems. The correct description of cryptic merle is a problem when registering the dog. These dogs appear like normal colored and are usually registered as non-merle dogs since not every breed registry color code includes the merle pattern as a choice.

Frequent mistakes: Excessive white markings in puppies from a tri-to-merle cross are not an indication that the puppy is a cryptic merle. The genetics of excessive white markings is completely different and have nothing to do with merle gene.

In breeding, a cryptic merle can be mated only with non-merle dogs (like dogs with regular merle allele). When crossed, the cryptic allele may expand again to regular non-shortened merle allele.  When mating a cryptic merle (Mc/N) with a non-merle (N/N) you can find puppies with the following genotypes: Cryptic merle/non-merle (Mc/N), Merle/ non-merle (M/N), non-merle/non-merle (N/N).

Hidden merle

Hidden merles are merle dogs who do not exhibit the merle pattern because their coat color does not show the pattern. Merling is not normally shown in red, gold, fawn and cream coat colors.  The hidden merle can be distinguished only by a genetic test.

Recessive red and merle can be a dangerous combo, simply because you may not know that a recessive red dog is a merle. The two genes occur together in a number of breeds, including Pomeranians and Chihuahuas, and in such breeds it's advisable to never breed a clear red dog (with any merle in its ancestry) to a merle, due to the risk of accidentally breeding double merles. Getting your dogs tested for Merle eliminates this problem.

Clear sable can "hide" merle almost as effectively as recessive red. A clear sable is one with no dark (eumelanin) hairs in its coat, and clear sables may be almost indistinguishable from recessive reds. For this reason, care should be taken when breeding any solid red dogs in breeds where merle is present.


Genetic testing for merle gene is highly recommended in order to avoid severe health problems that may occur when merle, cryptic merle and hidden merle dogs are crossed incorrectly or in case of risky breeding. The genetic test reveals the merle, the hidden merle and the cryptic merle variants.

All puppies that appear as "non-merle" at first sight have to be properly checked for any less visible merle patches. If such patch is found, it is not a non-merle, but a cryptic merle. In particular, the small merle patch can disappear in long or thick hair. Later, such dog can be mated with another cryptic/hidden merle dog unintentionally. So the breeders can run unintentional risks of producing double merle dogs.

Merle Modifiers

A merle modifier is a gene that, when inherited along with merle, will affect the way the merle pattern appears. A dog with a merle modifier but no merle gene will not be affected at all. It's thought that merle modifiers are inherited separately from merle and appear on their own locii. Merle Modifiers: Tweed, Harlequin, & Pseudo Harlequin