Why DNA Testing is Important for Breeding
I DNA test my puppies for both health and traits to make the best breeding decisions. One crucial trait I need to know is whether a dog carries the Merle gene, as this can impact both appearance and breeding choices. My first two Bernedoodles were visibly merle: one with a classic blue merle coat—gray with black spots—and the other with gray, black spots, brown accents, and one blue eye.
Discovering Double Merle in My Bernedoodle
I planned for both of these dogs to be the mothers of my new Bernedoodle breeding business. After checking their DNA for health and coat traits, I learned my dog Coco was Mm—she had one merle gene and one non-merle gene. This is typical for a merle dog; a single 'M' gene is enough to produce the merle pattern.
When I tested Kira, her results came back as M/M**, meaning she has two merle alleles. This concerned me, as I’d heard that double merle (MM) dogs can face health risks, such as deafness, blindness, and a lack of pigmentation (often appearing mostly white). However, Kira is healthy and doesn’t exhibit any extreme merle traits. I began researching to understand what could be going on.
Understanding Merle Variations
Much of my knowledge on this topic comes from the fantastic resource at DogGenetics.co.uk, which explains that Merle comes in several variations. Some merle types can pose risks when bred with another merle dog, while others are less likely to cause issues. There are actually six known types of Merle: Mc (Cryptic), Mc+, Ma, Ma+, M (Standard), and Mh (Harlequin). In this post, I’ll focus on Mc (Cryptic Merle) and M (Standard Merle), as these are the types most relevant to breeding decisions.
What is Merle, and How Does It Affect Coat Color?
Merle is a harmless genetic anomaly in itself, affecting coat color by adding an extra segment of DNA to the genome. This extra DNA can vary in length, which creates different merle types. The merle gene likely originated from a single ancestor and has spread throughout dog breeds over generations.
The merle gene dilutes or “lightens” the base color (black or brown), creating a "spotted" appearance. A merle dog will often look gray or tan with patches of its base color. However, double merle dogs (MM) can be at risk for health problems, as excessive dilution can affect pigmentation in the skin, eyes, and ears, leading to blindness or deafness.
Breeding Safely with Merle: Why Kira’s Litter Wasn’t All Spotted
It’s safe to breed a double merle dog with a non-merle (m/m) dog because each puppy will inherit only one merle gene, making them Mm. When I bred Kira, I expected her entire litter to have a merle pattern. However, not all of the puppies were spotted, which led me to hypothesize that Kira might carry one standard merle gene and one cryptic merle gene (Mc).
If Kira has both M (Standard Merle) and Mc (Cryptic Merle), she could pass down either gene to her puppies. Some puppies would inherit the visible merle trait (M/m), while others might inherit the cryptic merle (Mc/m) and look like non-merles but still carry the gene. Interestingly, one of Kira’s black and white puppies has blue eyes, which can sometimes be caused by the merle gene.
What Is a Hidden Merle?
Hidden merles typically refer to red or golden dogs that carry the merle gene but do not show it. This happens when the dog has a red (ee) coat, which is recessive and requires two copies of the e gene. A dog with ee will display a red coat that can mask any merle pattern. If you plan to breed a merle dog with a red or golden Bernedoodle, make sure the Bernedoodle is DNA-tested, as hidden merles can still carry the gene without displaying any merle patterning.
Why Red Coats Mask Merle and Other Colors
When a dog inherits two e genes (ee), the red coat color overrides other coat color genetics, including merle and tan points. This is why a red-coated Bernedoodle with the merle gene might not look like a merle at all. In cases where both parents carry the red gene, it’s even possible for a golden or red Bernedoodle to produce a litter of entirely red-coated puppies.
Future Hopes for Merle Testing
As of now, many DNA testing companies, such as Embark, can detect the presence of the merle gene but don’t differentiate between types. This is why I’ve sent a sample from Kira to UC Davis for further testing, as they can measure the length of the merle allele, helping to confirm if she carries a cryptic merle gene. Understanding the exact type of merle will improve breeding decisions by allowing breeders to identify safe pairings more accurately. Hopefully, more companies will offer these detailed merle tests in the future.
Final Thoughts: Better Safe Than Sorry
For now, it’s best to err on the side of caution when breeding merle dogs, especially when there’s any uncertainty about merle types. Testing and understanding these genetic traits help us breeders make responsible choices to promote healthy puppies.
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