Have you seen those strikingly colored dogs that turn heads as they walk down the street? If you consider yourself a "dog person", you probably know that this coloring is called “merle”.
This is a blue merle Border Collie named “Ego”.
What most dog people do not know is how breeding these colored pooches work. These dogs are in high demand, and rightfully so, due to their beautiful color patterns. Yet breeding these unique looking pups is a balancing act, and done incorrectly can cause health problems and even death.
While merling is a color pattern, it is also a gene. That is where the problems come from. The merle gene is dominant: it will trump a different colored gene. In the breed of Australian Shepherds, for example, there are 4 main color patterns: Red Tri, Black Tri, Blue Merle, and Red Merle. A tri-colored dog is represented in a Punnett square as mm (two recessive genes), where a merle colored dog is represented as Mm (a dominant and a recessive).
When you breed a tri colored dog to a merle colored dog, you only have a 50% chance of getting merle colored dogs, and 50% chance of getting tri colored dogs. This doesn’t mean that half the litter with be merle and half will be tri. It does mean that each individual puppy has a 50/50 shot.
A black, white, and brown solid dog like “Frankie” shown here is often less popular than the uniquely colored dog like “Ego” from before with splashes, fades of color, and speckles. This creates breeders who want to have more merle colored puppies so they can sell more dogs.
Common sense tells breeders: if merle is a dominant color gene, why don’t we breed 2 merle colored dogs and increase our odds? Sure, that could work. But the thing is ... When you breed two merle colored dogs you get puppies with 50% Mm (merle), 25% mm (tri) and 25% MM (double merle). This double merle is a dog that possess both dominant merle genes, a SUPER DOG! ... Except, not really.
When we get these dogs that are double merles, we run into genetic defects. Double merle dogs; while it is a gene and not a color per se, are typically described as mostly white, with light, sometimes minimal merling patterns. Due to this lack of pigment, the dog is prone to hearing and sight issues.
Dogs are able to hear because of pigment that develops inside the ear. When this pigment is absent, the dog becomes hearing impaired, or worse, deaf.
A dog’s eyes need pigmentation to develop, and again, with the lack of pigment due to the double merle gene, these dogs are susceptible to a number of eye defects. Microphthalmia, subepithelial, corneal dystrophy, displaced pupils, colobomas, and microphthalmos are just some of the eye-health issues double-merled dogs can face. Some of these double merle dogs are dubbed “lethal whites” because they have such severe genetic defects that they die before they are born or shortly after.
But don’t fret! There is an extremely easy solution for this: don’t breed two merle dogs!
A majority of people who breed two merle colored dogs are completely unaware of the genetics problems that come with double merle puppies. Be an advocate for these uniquely colored dogs! Due to these puppies being “unwanted” by breeders and owners, many find themselves in shelters and rescues looking for homes.
While owning a vision or hearing impaired dog may be a challenge, it is not impossible; many of these dogs are thriving in homes that have adapted and worked with their special needs. When purchasing a puppy, don’t be distracted by color; pick a dog based on personality, compatibility to your lifestyle, and overall health and longevity of the dog. Tri-colored dogs are essential to successfully breeding healthy merle dogs.
Reach out and educate.
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