Merles! Merles! Merles!

Shortened Versions of the Merle Locus

Genotype for Merle Gene: [M, Mc, Mc+, Ma, Ma+, Mh, m]
DNA RESULTS for the Merle Pattern will vary according to the lab you use.

Some terms and definitions to help in understanding.
MERLE: a SINE insertion on the SILV gene.
SINE: Short Interspersed Element. Lives off the host and can change the function of a cell.
LINE: Long Interspersed Element
INTERSPERSED ELEMENT: breaks this linkage, allowing independent creation of a new gene.
PATCHWORK: a merle modifier that turns the diluted parts of the coat into different shades of brown, grey and tan.

Dr. LA Clark first identified the Merle mutation in 2006.

Both SINEs and LINEs are common in canines and all mammals, including humans. They can be destructive or sometimes useful. Most SINE insertions occur in areas of the genome where they cause no damage or change. Occasionally SINEs insert in regions where they can alter expression.

For the Merle mutation, a SINE insertion impairs the cells ability to produce normal pigment. The Merle SINE mutation consists of 3 parts, a head, a body and a poly-A tail. The tail contains a long string of repeating base pairs.

Originally, the Merle test identified the body of the Merle mutation and was assumed any length of tail produced the Merle pattern. So any length of Merle was reported as a full Merle. But research showed the longer the tail the more Merle Pattern was produced on the body.

Now we understand that there is a length of Merle so shortened that it can not cause a change to the coat pattern. As time went on, test results were given using Mc, indicating that the mutation was not a full Merle but a shortened one.

Eventually, Dr.'s in paying attention to the length of the poly-A tail, found that there was also a third length of Merle which was longer than Mc, but shorter than the full Merle. So now we have 3 different lengths of the Merle. Add the Non-merle type and we have 4 separate alleles on the M locus.

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. 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.

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.

 

Examples of Mc Merles

Mc Merle produced by Craig Olszewski
Blue Tri Cryptic Merle Blue Tri Cryptic Merle Blue Tri Cryptic Merle
 Blue Tri Cryptic Merle Blue Tri Cryptic Merle
Mc Merle produced by Solid stone Bulldogs
Black Tri Crypric Merle Puppy Black Tri Crypric Merle Puppy
 
Credits: All information was excerpted from different readings, articles, websites, etc. from educated, scientific sources, combined with my own research.
Merle - SINE Insertion from Mc - Mh
Merle - SINE Insertion from Mc - Mh
Dr.Helena Synkov'a
Dr. Beatrix Böckmann
 
 
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