What is Merle?

The merle pattern is the result of pigment reducing genes. It modifies the color gene to decrease pigment in the hair, skin, ears and eyes, If pigment is reduced in the ear, the hairs responsible for hearing [stria] die. Since merle is a pigment reducing gene every merle dog has the potential to cause eye and hearing problems.

One of the biggest differences in the merle pattern from other color genes is it’s ability to reduce pigment. Other color genes add color while this one takes the color away, and that is what could cause problems. Pigment reducing genes cause these problems in a congenital way, that means it happens at birth, and it’s not hereditary. Merle is a mobile bit of DNA, and can move around that is why you will not see any uniformity in the pattern it causes.

Some of the consequences of this pigment reduction can be in both heterozygous merle (Mm) and homozygous double merle (MM). These dogs may exhibit auditory and ophthalmic abnormalities including mild to severe deafness, increased intra ocular pressure, ametropia, microphthalmia and colobomas. The double merle genotype may also be associated with abnormalities of skeletal, cardiac and reproductive systems. {GENMARK}

For those of us that care about the welfare of the breed , this is our greatest adversary. The merle Chihuahua is the result of back yard breeder greed. Taking another breed and adding it to the Chihuahua gene pool while calling this a purebred dog, is in this author's opinion unethical, and unconscionable. Not only does this rob the breed of the essence of what is a Chihuahua, which is called breed type, it is adding a gene that can cause eye and hearing problems. This is not a fancy color, this is a genetic mutation that functions much like a virus inserting itself in the DNA strand and removing pigment.

One of the biggest reasons merle is so dangerous in the Chihuahua breed is because we allow all colors. Merle coupled with certain color combinations can cause the same defects as breeding two merles together. This can be especially true of the piebald gene. Visual color breeding in this breed is virtually impossible, you can breed a merle to a solid and still end up with a piebald merle, so adding merle to this breed, in this authors's opinion, is inhumane.

This begs the question, "why would anyone add this to a breed on purpose?"

In many of the books on breeding canines their authors caution novices to leave the breed better then they found it. When asked, merle Chihuahua breeders have come up silent on how this pattern will improve the breed, which is not surprising considering there is no benefit to the breed at all. Breeding one dog that has the above photo defect, [micropthalmia] or any of the others listed is not worth this pattern.

Please note: Ocular abnormalities that may be seen with ocular dysgenesis and merling with excessive white in the coat, include microphthalmia, microcornea, heterochromia irides, cataract, staphyloma, retinal detachment, irregular pupil, white to blue iris (albino), angle dysgenesis, iris coloboma, blindness, and absence of tapetum lucidum. Tapetum lucidum is a reflective substance that lines the back of the dogs eyes. This reflective structure acts like a mirror and reflects light back through the retina, like a satellite dish giving the retina two chances to catch the light. Dogs that lack tapetum licidum have night blindness or reduced ability to see in low light such as the dog below.

Merling is inherited as a dominant trait. Heterozygotes for merling [single merles] have merle or dappled coats and occasional eye abnormalities. Homozygotes [double merles] have predominantly white coats and frequent eye abnormalities

If you came to this page on a search for a puppy, there is one thing you can do to help our breed. Refuse to buy into the hype of the merle Chihuahua and never buy a Chihuahua puppy this color. If there is no demand some may abandon their merle breeding plans. There are so many healthy lively colored Chihuahuas to choose as your next companion so there is no need to set yourself up for heartache. You can save yourself and the breed unnecessary suffering. This is not a special rare color, it is a genetically defective gene that was never in the breed until some added it for profit.

Ask yourself this question, "What is more important for the future of our breed, a color pattern that can come with genetic defects, or a minor change in the standard to protect its health and breed type?

Conscientious breeders should not knowingly breed bad patellas, leg perthes, cardiac problems or known genetic DEFECTS and merle falls right into this category. New people to the breed need the influence and knowledge of educated breeders so that they will understand how detrimental merle is to this particular breed. The show ring DQ is only a tool, to show that merle is an undesirable trait in Chihuahuas, and it is a first step towards education.

The problem with breeding merle is: just because the offspring are not merle they can still carry the alleles for the problems caused by the merle gene and that can pass down to generation after generation of their ancestors. Don't believe that? Read the Australian Shepherd site and some of the newer articles by CA Sharp. http://www.ashgi.org/index.htm

Before the merle gene was mapped it was always suggested that the problems caused by the merle gene were congenital rather than hereditary such as colobomas , absence of the tapetum lucidum etc, but since they now know that merle is a "jumping gene" [retro transposon] it can pair up with other genes all along the genome and the dog produced does not have to be merle. Its like a computer virus inserting itself into the DNA and wreaking havoc within the gene pool. Those that are breeding this gene in Chihuahuas, because they superficially admire the color are IMO modern day typhoid Marys. Their pedigrees are to be avoided.

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"In a breed standard, breed type should prevail over a color pattern....."

©Gloria Lambert 2007