Merle Bulldog Color

English & French Bulldogs

Genotype for Merle Bulldog is: [MN]

According to the lab you use, DNA info for the Merle Pattern is Mm or MN.

Random hair strands are diluted to a lighter shade by the merle gene, leaving behind patches of the original color. Because the Merle Gene is inherited from a black bulldog, you will have a black bulldog with Merle markings. In contrast to the piebald design, the outer margins of the patches may appear jagged. Pheomelanin (red) is unaffected by Merle, which only affects Eumelanin. Any black, liver, blue, or lilac in a bulldog’s coat, eyes, or nose will be merled.

Because of the varying shades of blue or grey in their coat, Black Merle canines are also referred to as “Blue Merles.” Although the phrase “blue merle” is commonly used, it is incorrect. They should be referred to as black merle in the proper jargon. Their eyes are either brown or blue, and their nose pigment is black. A merle bulldog would be completely black if they didn’t have the merle gene. The term “Blue Merle” is deceptive since it implies that these canines have blue pigment (dd) when they have black. Visually, dogs are defined by their PATCHES, which help determine their color and what it should appropriately be called. 


M, Mc, N

Coat patterns that are not dominant, such as Merle, are defined by patches of diluted pigment mixed with a solid color. Merle bulldogs often have eyes that are blue or partially blue. A SINE insertion in the Pmel17 or Silver (SILV) gene is what produces Merle.

As Eumelanin (the black pigment) is absent in dogs with the MC1R ee genotype (recessive red), they do not produce Merle, but they can still produce Merle-positive offspring.

It is possible to have one of three alleles (variants) of the merle gene:

  • The M allele
  • The Mc allele (cryptic merle)
  • The non-merle merle allele (N allele, no SINE insertion)

It is not uncommon for french bulldogs or English bulldogs with cryptic merle, distinct from phantom merle or ghost merle, to display little to no merling.

Both M and Mc alleles of the merle gene are susceptible to genetic mutations. M can occasionally undergo poly-A tail reduction to create Mc during DNA replication and cell division.


M/M 2 copies of merle are present (double merle)

M/Mc 1 copy of merle and one 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 


The merle gene contains an additional segment of DNA known as a SINE insert. Patches of color appear on dogs with this SINE insertion, preventing average pigment production. The length of the SINE implantation is adjustable. It has a more significant impact on the dog’s coat when it’s longer. The shortest one is 200 characters long, while the longest is 280 characters long, as illustrated below.


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

The Merle Pattern’s DNA results will differ depending on the lab you use.

Alleles on the M Locus of Merle testing by Biofocus are presented below.

1. Full Merle M, the longest

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

3. Short Merle Mc, so short that Merle can no longer express.

4. Non-Merle m, no SINE insertion.

Note: It is possible for a dog that tests Ma/Mc through Biofocus to test McMc at other labs that do not include the Ma allele in their testing. Because an M/Ma dog is known as a Patchwork dog, this would be perplexing for the breeder. Aside from that, it is impossible to shorten M, Ma, or Mc to m (non-merle). The DNA would have to be removed entirely, which cannot happen.

Now for even more confusion. Neither Merle’s Shortening nor its Lengthening is steady. Thus, the Poly-A tail might vary in length from parent to offspring.

In the case of a Full Merle parent, the Merle Poly-A tail can shorten to Ma or Mc, and every M Merle dog of any breed can do so. Merle’s Poly-A tail could also grow longer from parent to offspring.


Merle testing by Vemodia has given us seven alleles on the M Locus.


m: Non-Merle – Wild Type. No Merle pattern–solid coat 

Mc: Cryptic Merle, 200 – 230 bp. No Merle pattern–solid coat 

Mc+: 231 – 246 bp. No Merle pattern–solid coat 

Ma: Atypical Merle, 247 – 254 bp. No Merle pattern–diluted–brownish hue 

Ma+: 255 – 264 bp. Muted, undefined, diluted–brownish hue 

M: Merle, 265 – 268 bp. Classic Merle 

Mh: Harlequin Merle, 269 – 280 bp. Minimal Merle, areas deleted to white, tweed 

Dogs with three or four alleles on the M locus have been found in Mosaic research results. For example, as M/Ma/Mc.


When the Merle Gene is expressed, it dilutes random portions of the bulldog coat to a lighter shade, leaving behind patches of the original color. Adding the Merle Gene to a black dog results in a dog that is genetically a black dog but genetically diluted. In contrast to the piebald pattern, the outer edges of these patches or sections may appear jagged. Only Merle affects Eumelanin; Pheomelanin (red/fawn) remains unaffected and will appear normal. So, if you have a merle bulldog, you won’t be able to notice it. Only black-based coat colors are affected by Merle. Eyes and noses can also be merled.

Because of the Merle gene’s ability to dilute areas of black to a grey color, black Merle dogs are commonly referred to as “Blue Merles.” genetics of the Black Merle breed The phrase “Blue Merle” is widely used. However, it is incorrect. Merle Bulldog Nose, footpad, and eyeliner pigment are still black. Therefore, they should be referred to as Black Merle. These canines would be completely black without the merle gene. To describe a black dog as blue merle is deceptive because actual blue dogs should have the [dd] gene. A black merle dog will never carry the double [dd] gene, while a True Blue Merle dog will always have it. Visually, a dog’s color and proper name affiliation are determined by the patches on its body. DNA tests can verify this. As a result, in a True Blue Merle dog, the intact patches are True Blue, while the diluted areas are a much lighter blue. This is the case in all the Rare Colors. Because the lilac Merle bulldog’s coat is so light, the remaining patches are virtually white. Upon reflection, this makes perfect sense. A Lilac Merle dog has three dilution genes at play. In some cases, DNA Color Testing may be required to determine the actual color.

Unhealthy Breeding Issues With Merle Bulldogs

When the Merle gene is duplicated, it can, but does not usually, result in health problems, the most common of which are hearing loss and blindness.

As a result, breeding two merles should be avoided because the result could be Merle puppies with health issues. These issues are nearly nonexistent in dogs with only one Merle gene, and the prevalence rate is the same regardless of the breed, color, or pattern. Double Merle can be an issue since it can produce a lack of pigment in some essential regions of the bulldog, such as the eyes and inner ears. Due to the presence of a non-merle gene, single merle dogs nonetheless have an abundance of pigmentation. Double Merles are known for having vast patches of white when no pigment is created.

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. Therefore, it is vital to know the TRUE DNA of your dog if you plan to breed.

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