We use UC Davis for our MERLE Testing
https://www.vgl.ucdavis.edu/services/dog/Merle.php
This page is not just my opinion. Every word on this page has been taken from articles of Scientists, Geneticists, Doctors, etc. all of which can be found by the links at the bottom of this page. It took me 5 months to read and go through all the websites and articles and excerpt the pertinent info that applies here.
So many people want to swear that English Bulldog breeders are mix breeding and hanging papers to get Merle Bulldogs. Most believe whatever they are told, or what they read without any backing to prove the belief, yet they still believe it and will actually accuse others of wrongdoing without any facts to back up the accusation.
That is pretty sad since there are many VERY reputable breeders that have a conscience and ethics....so I have compiled some info here, that can be backed up with science, and by Professionals with the education to state what is correct.
We are not so misinformed, though that we do not realize that there are breeders who HAVE cheated, mixed, and hung AKC papers taking shortcuts to get the Merle in their program. This makes it even harder for the ethical breeder of Purebred AKC Merle English Bulldogs.
As for our breeding program, we have parentage DNA with AKC on all our dogs associated with our Merle Program. Our Merles are PUREBRED AKC Bulldogs (English Bulldogs). AKC themselves list ALL Breeds in connection with the Merle pattern as do others as you will see below.
Hidden Merle Facts
Merle can be hidden by other genes, and patterns, sometimes for long periods of time. This is why the merle gene can and has ALWAYS been in EVERY breed and is backed up by scientific fact.
Hidden merles are merle dogs who do not exhibit the merle pattern because their coat color does not show the pattern. Merling is not normally shown in red, gold, fawn and cream coat colors. The hidden merle can be distinguished only by a genetic test.
1. Recessive Red: Merle can be completely hidden by recessive red, as recessive red dogs can't make eumelanin pigment and merle only affects eumelanin. A recessive red merle is known as a phantom, ghost, or cryptic merle.
2. Sable: A clear sable (dog with a red coat, but no visible black sabling) will also not show any merling because there is no eumelanin to be merled, unless it also has a mask (which does show merling).
Shaded sables will often show merle at birth, but it tends to fade as the dog grows up, so all that remains on an adult is usually a few darker brownish patches on the coat (which can be hidden very easily by thick or long fur).
3. The greying gene can also make it very difficult to see merle markings.
4. The dilution gene (dd), can also hide the merle because it dilutes the patches to roughly the same color as the base.
5. Brindle: Merle can be very difficult to see on a brindle too, due to the stripes. Brindle can hide merle, merle can hide brindle, or they can mix.
6. Heavy Markings: Merle can be hidden if the dog has very heavy markings, so a black merle could appear completely black if the patches are large enough (a cryptic merle).
Partial Excerpt from the UCDavis Website
https://www.vgl.ucdavis.edu/services/dog/Merle.php
Merle is an incompletely dominant coat color pattern characterized by irregularly shaped patches of diluted pigment and solid color.
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 (germline rate of 3-4%) while Mc may undergo expansion and revert to M. Because of the complexities of merle inheritance, and potential health concerns, DNA testing is recommended to establish the genetic make-up of dogs for the merle gene for those breeds where this color dilution pattern is present.
The Veterinary Genetics Laboratory is licensed to offer the merle test.
Results are reported as:
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
References: Clark LA, Wahl JM, Rees CA, Murphy KE. Retrotransposon insertion in SILV is responsible for merle patterning of the domestic dog. Proc Natl Acad Sci U S A. 103(5):1376-1381 (2006). Kaelin CB, Barsh GS. Genetics of pigmentation in dogs and cats. Annu. Rev. Anim. Biosci. 1:16.1-16.32 (2013).