This site contents and graphics are original & copyright protected 2004-2009
MERLES
MERLES
In January 2006, scientists at Texas A&M University announced the discovery of the way in
which the Merle gene occurs in dogs.
The Merle gene was found to be caused by a mutation in the gene called SILV or PMEL17.
The way the mutation occurs is called retrotransposon.
This is the ability for a piece of your dogs DNA to actually jump out of the gene it has
infected during cellular division and genetic DNA replication. When the melanocytes (black
pigmentation genes) are migrating from the neuronal crest during the embryonic
development of the Chihuahua the Merle gene removes itself from the melanocyte genes
and like a parasite invades and infects the eumelanic gene (the gene which produces
black, blue or grey, dark brown(chocolate) & liver color) areas in the coat.
This Merle parasitic attachment acts to lighten whatever coat color would otherwise have
been seen. Normal dilution genes will lighten the entire coat, but the Merle is expressed as
patches of diluted color scattered over the dog’s body which gives a mottled or uneven
speckled effect
This is NOT the ticking which is sometimes seen in the Chihuahua breed. Ticking is NOT
harmful to the Chihuahua breed.
The Merle gene when heterozygous Mm (only one copy of the gene) on an otherwise black
dog produces a blue Merle which is phenotypically (what you see) as a bluish gray dog that
has the uneven full color black spots. A homozygous or MM dog (carrying two copies of the
Merle gene), often called a double Merle or a homozygous Merle will be a mostly white dog
(similar to an extreme Piebald). Frequently these white dogs are deaf and/or blind.
This is an example where genes involved in pigmentation of hair or skin can also be
associated with development of nerves. Most breeders have learned to avoid this problem
by never breeding two Merle dogs together.
The normal state of the Merle locus is dual recessive mm and completely lacks the
offending transposon resulting in normal color non Merle dogs.
The Merle locus is autosomal (not carried on one of the sex chromosomes) acting as a
dominant mutation (it is seen in all dogs that carry this gene).
It should also be noted that genetically such transposons do not arise
spontaneously but must be passed from sire and/or dam to their offspring.
This means that if the Chihuahua did not carry this allele to begin with, then only through
breeding to another breed, that does carry this transposon, would allow for it to be
integrated into the Chihuahua genome.
There are four issues of concern with the Merle as a color pattern in the
Chihuahua breed:
1.The Merle pattern in the Chihuahua may have come about through unethical
breeding to another breed of dog. This practice would then have been followed
by falsely registering such a mongrel as a purebred AKC Chihuahua.
2. The other issue is related to the health aspects of the Merle allele. See below.
3. Most dog breeds do not even carry a Merle gene. Little in his book never had Merle
as a possibility for the Chihuahuas so it could not have Mutated when their was not
a gene here in the first place. It was not know in the Chihuahua breed.
The animal that would have been used to introduce the Merle gene would have
came with its' own breed specific problems that will now become a part of the
Chihuahuas breed specific problems.
4. Another problem with allowing the Merle color in Chihuahuas is that we have so
many light-colored dogs. In the breeds that have Merle as an acceptable
color/pattern their color pool had to be modified to just a very few colors in order
to keep from having the hidden/Cryptic Merle that would become invasive and
would allow for the doubling up of the Merle gene unknowingly. These Merle are
often NOT recognizable as Merle as adults.
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.
The Chihuahua standard reads, "any color solid, marked, or splashed."
This refers to color, not modifiers that act on color causing a pattern.
Splash may have the appearance of Merle but it is GENETICALLY NOT a Merle it is a color
and not a modifier.
The Merle gene is a modifier producing a pattern, not a color.
The Merle gene modifies, or acts on, any color it is paired with.
Once this parasitic gene enters our Chihuahua gene pool it will not be detectable to the eye
and it can easily creep into any line through a breeding to a different Chihuahua line rather
than using your own "safe" Merle free line. Just looking at the pedigree of the Chihuahua is
of little value because the Chihuahua changes color and unless the breeder was very
observant and noted any Merle spot as Merle when the pup was first born then it can be
hidden as the pup grows older.
Below is a link to one person's experience with breeding Merle Chis, is this really worth it?
http://www.kandeechihuahuas.com/merles/ftlowille.html
NEWS UPDATE: The test that was available to test for the Merle gene is false. The
company is out of business. So just when you thought we could properly identify the Merle
we are back to square one are not able to identify any hidden MERLES.
Article Resources For The Trouble With Merle
1. http://en.wikipedia.org/wiki/Merle_(coat_color_in_dogs)
2. http://homepage.usask.ca/~schmutz/merle.html
3. http://www.geocities.com/coatcolorindogs/index.htm
4. http://www.pnas.org/cgi/reprint/0506940103v1
5. http://www.apbtconformation.com/merle.htm
6. http://www.gi.alaska.edu/ScienceForum/ASF8/826.html
7. http://www.biomedcentral.com/1746-6148/2/9
8. http://www.genmarkag.com/canine_faqs.php
9. http//www.diademchihuahuas.50megs.com/favorite_links.html
10. http://mysite.verizon.net/res8w765/id23.html
11. http://www.pubmedcentral.nih.gov:80/articlerender.fcgi?artid=1431520
Link to CCA Website for CCA Merle breeding guidelines
In January 2006, scientists at Texas A&M University announced the discovery of the way in
which the Merle gene occurs in dogs.
The Merle gene was found to be caused by a mutation in the gene called SILV or PMEL17.
The way the mutation occurs is called retrotransposon.
This is the ability for a piece of your dogs DNA to actually jump out of the gene it has
infected during cellular division and genetic DNA replication. When the melanocytes (black
pigmentation genes) are migrating from the neuronal crest during the embryonic
development of the Chihuahua the Merle gene removes itself from the melanocyte genes
and like a parasite invades and infects the eumelanic gene (the gene which produces
black, blue or grey, dark brown(chocolate) & liver color) areas in the coat.
This Merle parasitic attachment acts to lighten whatever coat color would otherwise have
been seen. Normal dilution genes will lighten the entire coat, but the Merle is expressed as
patches of diluted color scattered over the dog’s body which gives a mottled or uneven
speckled effect
This is NOT the ticking which is sometimes seen in the Chihuahua breed. Ticking is NOT
harmful to the Chihuahua breed.
The Merle gene when heterozygous Mm (only one copy of the gene) on an otherwise black
dog produces a blue Merle which is phenotypically (what you see) as a bluish gray dog that
has the uneven full color black spots. A homozygous or MM dog (carrying two copies of the
Merle gene), often called a double Merle or a homozygous Merle will be a mostly white dog
(similar to an extreme Piebald). Frequently these white dogs are deaf and/or blind.
This is an example where genes involved in pigmentation of hair or skin can also be
associated with development of nerves. Most breeders have learned to avoid this problem
by never breeding two Merle dogs together.
The normal state of the Merle locus is dual recessive mm and completely lacks the
offending transposon resulting in normal color non Merle dogs.
The Merle locus is autosomal (not carried on one of the sex chromosomes) acting as a
dominant mutation (it is seen in all dogs that carry this gene).
It should also be noted that genetically such transposons do not arise
spontaneously but must be passed from sire and/or dam to their offspring.
This means that if the Chihuahua did not carry this allele to begin with, then only through
breeding to another breed, that does carry this transposon, would allow for it to be
integrated into the Chihuahua genome.
There are four issues of concern with the Merle as a color pattern in the
Chihuahua breed:
1.The Merle pattern in the Chihuahua may have come about through unethical
breeding to another breed of dog. This practice would then have been followed
by falsely registering such a mongrel as a purebred AKC Chihuahua.
2. The other issue is related to the health aspects of the Merle allele. See below.
3. Most dog breeds do not even carry a Merle gene. Little in his book never had Merle
as a possibility for the Chihuahuas so it could not have Mutated when their was not
a gene here in the first place. It was not know in the Chihuahua breed.
The animal that would have been used to introduce the Merle gene would have
came with its' own breed specific problems that will now become a part of the
Chihuahuas breed specific problems.
4. Another problem with allowing the Merle color in Chihuahuas is that we have so
many light-colored dogs. In the breeds that have Merle as an acceptable
color/pattern their color pool had to be modified to just a very few colors in order
to keep from having the hidden/Cryptic Merle that would become invasive and
would allow for the doubling up of the Merle gene unknowingly. These Merle are
often NOT recognizable as Merle as adults.
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.
The Chihuahua standard reads, "any color solid, marked, or splashed."
This refers to color, not modifiers that act on color causing a pattern.
Splash may have the appearance of Merle but it is GENETICALLY NOT a Merle it is a color
and not a modifier.
The Merle gene is a modifier producing a pattern, not a color.
The Merle gene modifies, or acts on, any color it is paired with.
Once this parasitic gene enters our Chihuahua gene pool it will not be detectable to the eye
and it can easily creep into any line through a breeding to a different Chihuahua line rather
than using your own "safe" Merle free line. Just looking at the pedigree of the Chihuahua is
of little value because the Chihuahua changes color and unless the breeder was very
observant and noted any Merle spot as Merle when the pup was first born then it can be
hidden as the pup grows older.
Below is a link to one person's experience with breeding Merle Chis, is this really worth it?
http://www.kandeechihuahuas.com/merles/ftlowille.html
NEWS UPDATE: The test that was available to test for the Merle gene is false. The
company is out of business. So just when you thought we could properly identify the Merle
we are back to square one are not able to identify any hidden MERLES.
Article Resources For The Trouble With Merle
1. http://en.wikipedia.org/wiki/Merle_(coat_color_in_dogs)
2. http://homepage.usask.ca/~schmutz/merle.html
3. http://www.geocities.com/coatcolorindogs/index.htm
4. http://www.pnas.org/cgi/reprint/0506940103v1
5. http://www.apbtconformation.com/merle.htm
6. http://www.gi.alaska.edu/ScienceForum/ASF8/826.html
7. http://www.biomedcentral.com/1746-6148/2/9
8. http://www.genmarkag.com/canine_faqs.php
9. http//www.diademchihuahuas.50megs.com/favorite_links.html
10. http://mysite.verizon.net/res8w765/id23.html
11. http://www.pubmedcentral.nih.gov:80/articlerender.fcgi?artid=1431520
Link to CCA Website for CCA Merle breeding guidelines
