Merle History of Rare Bulldogs

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MERLE

M, Mc, N

Merle is an incompletely dominant coat color pattern characterized by irregularly shaped patches of diluted pigment and solid color. Blue and partially blue eyes are typically seen with merle. Merle is governed by a SINE insertion in the Pmel17 or Silver (SILV) gene. 

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, while Mc may undergo expansion and revert to M. 

RESULTS (UCDavis) 

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 

BIOFOCUS

M, Mc, Mc+, Ma, Ma+, Mh, m

DNA RESULTS for the Merle Pattern will vary according to the lab you use. 

Merle testing by Biofocus gives 4 separate alleles on the M Locus as shown below.

1. Full Merle M, the longest

2. Atypical Merle Ma, a length between M and Mc.

3. Cryptic Merle Mc, a length so short that Merle can no longer express.

4. Non-Merle m, no SINE insertion.

NOTE: a dog that tests as Ma/Mc through Biofocus, would test McMc at other labs that have not yet included the Ma allele. This would be confusing to the breeder since a M/Ma dog is considered Patchwork. Also, M, Ma and Mc cannot shorten to m (non-merle). This would require the full removal of the DNA, which cannot happen.

Now for even more confusion. The Shortening and Lengthening of Merle is unstable. In other words, the Poly-A tail can shorten or lengthen from parent to offspring.

For instance a Full Merle parent can have puppies that are Ma or Mc, and every M Merle dog of any breed has the potential for the Merle Poly-A tail to shorten to Ma or Mc. The opposite can happen as well, Merle's Poly-A tail can lengthen from parent to puppy.

VEMODIA

Merle testing by Vemodia has now given us 7 alleles on the M Locus

VEMODIA CANINE TESTING

m: Non-Merle - Wild Type

Mc: Cryptic Merle, 200 - 230 bp

Mc+: 231 - 246 bp

Ma: Atypical Merle, 247 - 254 bp

Ma+: 255 - 264 bp

M: Merle, 265 - 268 bp

Mh: Harlequin Merle, 269 - 280 bp

There have also been Mosaic results with a dog having 3 or 4 alleles on the M Locus. For example as M/Ma/Mc. Whew! I will attack this in the Future.

The Merle Gene dilutes random sections of hair to a lighter color which leaves Patches of the original color, sometimes these patches can be very small. If you start with a black dog and add the Merle Gene, you still have a black dog genetically, but with sections of the black diluted. Unlike the piebald pattern, these patches or sections may look jagged on the outer edges. Merle affects only the Eumelanin, and does not affect the Phaeomelanin (red/fawn) which will appear normal. This means you can have a merle dog and not see it visually. Merle affects only black based coat color. Eyes, and noses can also be merled.

Black Merle dogs are often called Blue Merle because the Merle gene dilutes patches of black to a grey color. Blue Merle on genetically Black Merle dogs is a widely used term, but is not correct. They should be called Black Merle, their nose, footpad, and eyeliner pigment is still black. If these dogs did not have the merle gene, they would be solid black. The term Blue merle, when used on black dogs is misleading because blue dogs should have the [dd] gene if they were truly blue. A black merle dog will never have the double [dd] gene, but the True Blue Merle dog would always be [dd]. It is the patches on the dog that will visually define the dogs color and what it should be appropriately called. This can be backed up with DNA testing. Thus in the True Blue Merle dog, the patches that are left would be True Blue and the sections that are diluted would be a much lighter color blue. This is the case in all the Rare Colors. The sections left on the lilac Merle dog are almost white, it is so light. Makes since when you think about it. There are 3 dilution genes at work in a Lilac Merle dog. Some of these colors will blend in with the diluted color so much, that DNA Color Testing may need to be done to be sure of the true color.

The Merle gene when doubled up, can, but not always does, cause health issues, mostly deafness and blindness. For this reason, two merles should not be bred together, as this could result in double Merle puppies with possible problems. These problems are virtually eliminated in single Merle gene dogs and the percentage of incidence is the same as in any breed, color, or pattern. Double Merle can be problematic because it can cause lack of pigment in certain vital areas, such as the eyes and inner ears. Single merle dogs have plenty of pigment because they still have a non-merle allel to make pigment. Double Merles often have large areas of white where there is no pigment produced.

In the hierarchy of genes, the Merle Gene overrides the Dominant Black(SEAL) gene, the Seal gene overrides the black and tan gene, so you can have a Black and Tan, Black Seal, Black Merle dog and would mainly see only the merle, but muted. It is very important to know the TRUE DNA of your dog if you plan to breed.