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Merle Color Gene Fact Sheet by Graham Foote, Chairman of the British Chihuahua Club, divides the U.K. and AKC's Steve Gladstone over dog breeding ethics.


   Australia has banned the registration of merle Chihuahuas.

   Canada Disqualifies merle Chihuahuas from the show ring effective Jan 1st, 2008.

   England has banned the registration of merle Chihuahuas.

   Germany has banned merle Chihuahuas from breeding and the show ring.

   South Africa and Mexico are currently working on similar resolutions.


Graham Foote has bred Chihuahuas for over 40 years. His bloodlines are prized throughout the world. As an international judge, his opinions and evaluations are eagerly sought by show clubs, breeders, and exhibitors.


"As Chairman of the BCC, I would be astounded, if whoever it is that is trying to get our Kennel Club to change the ban on merle colour in Chihuahuas, has any success. All of our Chihuahua breed clubs had a free vote and in eight out of nine clubs in the country, the vast majority of members voted in favour of the ban.


"I believe our members voted in favour of the ban because we have never had merle Chihuahuas in the UK, and believe that our breed like most breeds have plenty of health related problems that need to be bred out, so why start to breed in new health problems and put our breed through unnecessary suffering?


"We have had the breed in the country since early in the 20th century, when they were mainly imported from the States. Practically all our breeding stock was lost in the 1940s, following the second world war, but a considerable number were imported from the states again in the early 1950s, so our lines originated from the States and over the years others have been imported from the States, yet we do not have the merle gene in our breed. I think that in general we accept the scenario put forward that this gene has been introduced in the States by crossing with other breeds, otherwise it would surely have shown up in our lines over the years.


"Even if not in particularly large numbers, it does on occasions appear to cause eye and hearing problems and I think all breeds with the merle gene present admit to this. It therefore seems to me to be cruel to let our Chihuahuas suffer to satisfy certain individuals vanity in their preference for a particular colour. We do not have the gene in other than a handful of Chis recently imported into this country from the states and I think no truly caring breeder will want to allow this gene to proliferate in the UK and this is no doubt why the vote against it was so strong.


"Going back to your original question of what I thought about Mr Gladsone's letter, only he knows what is behind it, but one thing for sure, it certainly is not the love of Chihuahuas."


Kind regards,

Graham Foote


Merle Gene Fact Sheet


Genetics of Canine Coat Color

Canine coat color is determined by the expression of a specific combination of genes. A gene, the basic unit of heredity, is comprised of a unique sequence of DNA and directs the production of a specific protein. Proteins are required for the structure, function and regulation of the body's cells, tissues, and organs. Genes are located within chromosomes. Dogs have two sets of 39 chromosomes in every cell, one set inherited from each parent. The location of each gene within a chromosome is referred to as its locus. While there is more than 99% DNA sequence similarity between dogs, variations in DNA sequence do occur in a small number of genes. Different forms of the same gene are called alleles. Dogs can have two identical or two different alleles for a particular gene. If both alleles are identical, then the dog is said to be homozygous at that gene; if both alleles are different, then the dog is said to be heterozygous at that gene. The genotype of an animal is its genetic identity, as identified by the alleles it carries; while the phenotype, or appearance, is the expression of those alleles. Coat color in dogs is usually controlled by a set of genes. These include the color genes, genes that affect the pigment color of hairs, and the pattern genes, those that affect the distribution of a particular color. At least 20 genes have been identified that affect coat color in dogs.


Merle Coat Color Patterning

The merle coat color is characterized by patches of dilute pigment in combination with areas of full pigmentation. Therefore, the merle gene acts to lighten whatever coat color would otherwise be expressed. However, unlike other dilution genes, the lightening effect is not spread evenly over the coat, but is expressed as patches of diluted color scattered over the dog's body. If the basic color of the dog is black, the effect of the merle gene is a soft gray, often referred to as "blue". If the basic color of the dog is red, the effect of the merle gene is a pale red. The merle coat pattern is characteristic of a number of breeds recognized by the American Kennel Club, including the Shetland Sheepdog, Collie, Border Collie, Dachshund, Australian Shepherd, and Cardigan Welsh Corgi.


Genetic Inheritance of the Merle Gene

It is only recently that investigators at the Texas A&M University (reference: PNAS, 2006, 103(5):1376-81) discovered a mutation in the dog SILV gene and found it to be responsible for the merle coat color patterning in dogs. The merle gene (M) is inherited in an autosomal fashion. In other words, the trait is not linked to gender and can be passed on from either the mother or the father. The gene is incompletely dominant, or a gene that has intermediate expression. A heterozygous dog, carrying only one copy of the merle gene (Mm), expresses the characteristic diluted coat color pattern. A non-merle dog (mm) is normal in color, while a homozygous double-merle (MM) is predominantly white. Punnett squares can be used to determine the expected coat color of offspring when breeding dogs of known genotype (i.e. coat color genes have been identified). In the example illustrated, a non-merle dog (mm), indicated in the vertical column, bred to a heterozygous merle (Mm), indicated in the horizontal column, will give rise to offspring with an expected frequency of 50% merle (Mm) and 50% non-merle (mm). Dogs that carry the merle gene but do not show the characteristic merle phenotype, are known as cryptic merles. These dogs may give rise to merle offspring. It is suspected that the DNA sequence of the merle allele in the cryptic is shorter than the allele expressed in the typical merle dog. The harlequin coat color pattern in Great Danes is produced through the interaction of the merle locus and the harlequin (H) gene. In harlequin Danes, the merle background color is diluted to nearly white with fully pigmented black patches.


Health Problems Associated with the Merle Allele - BOTH heterozygous merle (Mm) and homozygous double merle (MM) dogs may exhibit auditory and ophthalmic abnormalities including mild to severe deafness, increased intraocular pressure, ametropia, microphthalmia and colobomas. The double merle genotype may also be associated with abnormalities of skeletal, cardiac and reproductive systems.


Genetic Testing for the Merle Gene

With the recent discovery of the merle gene, a genetic test is now available that allows for the identification of the merle allele. This technology is patent pending (U.S. Serial # 60/708,589) and available exclusively thru GenMARK, the DNA technology service of VITA-TECH Laboratories LLC. By testing dogs for this genetic trait, it is possible to:

  • allow identification of merle dogs to prevent undesirable merle to merle breeding

  • classify harlequin Danes as single or double merle

  • identify cryptic merles

reprinted courtesy of


Related articles:

AKC Defended Board Member who interfered with Chihuahua Club ballot on merle color DQ.


Judge, British Chihuahua Club Chairman Graham Foote, on merle color gene  Fact Sheet.


Gladstone Letter to CCA Members to DQ merle color, using his AKC and AKC/CHF Board positions.


Chihuahuas - Any Color Marked Or Splashed?? Gloria Lambert, explains the genetic deformities.


Chihuahua Breeder Rebuts disqualifying merle colored, defends genetics, and thanks Gladstone.


Pomeranian Club Ignores AKC guidelines by adding merle pattern to Pomeranian breed standard.


World Bans Merle Chihuahuas refuse to register any dog out of merle parents.


Australian Chihuahua Breeder-Judge chastises AKC Director on his letter re merle gene.


Steve Gladstone Obituary the final link to a great man. Friend, attorney, advisor to the dog fancy, trusted AKC Board ally, founder of Aragorn Cardigans. EST 2002 17061802


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