What is the Difference Between Merle and Blue Merle?
The question of What is the difference between merle and blue merle? is often asked by dog enthusiasts. Essentially, merle refers to the overarching pattern, while blue merle specifically describes a merle pattern appearing on a dog with a black base coat, creating a swirling, diluted blue/gray appearance.
Understanding the Merle Gene
The merle gene (M) is a dominant gene that affects the eumelanin (black and brown) pigment in a dog’s coat. The merle gene causes random patches of color to dilute, resulting in mottled or patched patterns. This dilution isn’t uniform; some areas remain fully pigmented, while others become lighter, creating the distinctive merle look. Without the merle gene (m), the dog’s coat color remains unaffected. Dogs must inherit at least one copy of the merle gene from their parents to express the pattern. A dog with two copies of the merle gene (MM) is at higher risk for health issues, a concept called “double merle.”
Deciphering the Blue Merle Coloration
Blue merle is a specific expression of the merle gene. It occurs when the merle gene dilutes a black base coat (eumelanin). The black pigment isn’t entirely removed, but rather diluted to various shades of gray and blue-gray. This results in a coat with patches of solid black, shades of gray, and sometimes white markings. The intensity and distribution of the dilution can vary greatly, resulting in different shades and patterns within the blue merle classification.
Other Merle Color Variations
While blue merle is perhaps the most well-known, merle can affect other base coat colors. Common variations include:
- Red Merle (or Liver Merle): Occurs when the merle gene acts on a phaeomelanin (red/brown) base coat. The result is patches of liver (reddish-brown) color interspersed with lighter shades.
- Chocolate Merle: Similar to red merle, but involves a darker chocolate base coat.
- Brindle Merle: A merle pattern overlaid on a brindle coat (a striped pattern).
Dangers of Double Merle
Breeding two merle dogs together significantly increases the risk of producing puppies with double merle. Double merle dogs often suffer from severe health problems, including:
- Deafness
- Blindness
- Eye defects (e.g., microphthalmia)
- Other developmental abnormalities
Responsible breeders avoid breeding two merle dogs together to prevent these health issues. Genetic testing can accurately determine whether a dog carries the merle gene and how many copies they possess.
Recognizing the Merle Pattern
Regardless of the base coat color, the merle pattern generally involves:
- Randomly diluted patches of color
- Patches of the original base coat color
- Potential for white markings (often on the face, chest, and feet)
- Frequently, blue or partially blue eyes
It’s important to distinguish the merle pattern from other coat patterns that might appear similar, such as brindle or piebald.
| Feature | Merle Pattern | Brindle Pattern | Piebald Pattern |
|---|---|---|---|
| —————- | ————————————————— | ——————————————————- | ——————————————————- |
| Dilution | Random patches of diluted color | None (stripes of different colors) | None (except in merle piebalds) |
| Pigment Affected | Eumelanin (black/brown) primarily | Both Eumelanin and Phaeomelanin | Varies; typically white patches over base coat color |
| Pattern | Mottled, patched, diluted | Striped | Large, distinct patches of white |
Genotype vs. Phenotype
It’s crucial to differentiate between a dog’s genotype (its genetic makeup) and its phenotype (its observable characteristics). A dog may carry the merle gene (Mm or MM) but have a phenotype that is difficult to discern, especially if the base coat color is light or if there are extensive white markings. Genetic testing is the most reliable method for determining a dog’s merle status.
Frequently Asked Questions (FAQs)
What breeds commonly display the merle pattern?
Merle is found in various breeds, including Australian Shepherds, Border Collies, Great Danes, Dachshunds, and American Cocker Spaniels. However, it’s not universally accepted in all breeds, and some breed standards discourage or prohibit it.
Can merle dogs be registered with kennel clubs?
Registration policies vary significantly between kennel clubs. Some clubs readily accept merle dogs, while others restrict or prohibit their registration, particularly in breeds where the pattern is not traditional. Always check with the specific kennel club for their regulations.
How does the cryptic merle gene affect breeding?
Some dogs may carry a cryptic merle gene, also known as atypical merle. These dogs express the merle gene in a very subtle or barely noticeable way, making it challenging to visually identify them as merle. Breeding a cryptic merle to another merle dog can still produce double merle puppies, highlighting the importance of genetic testing.
Is the merle gene linked to any health problems besides deafness and blindness?
While deafness and blindness are the most well-known health issues associated with the MM genotype (double merle), affected dogs may also experience increased susceptibility to sunburn, skin cancer, and other eye problems.
What genetic tests are available to determine merle status?
Several genetic tests are available to determine a dog’s merle status, including tests that can identify the presence of the merle gene and determine the length of the SINE insertion, which can influence the expression of the merle pattern. These tests are typically performed using a cheek swab or blood sample.
Are all blue-eyed dogs merle?
No, not all blue-eyed dogs are merle. Blue eyes can occur in dogs without the merle gene, particularly in breeds with white markings or certain genetic predispositions. However, blue eyes are very common in merle dogs due to the gene’s effect on pigmentation.
How can I tell if a puppy is a double merle?
Double merle puppies often have a predominantly white coat, due to the extreme dilution of pigment. They may also exhibit physical abnormalities, such as unusually small eyes or misshapen ears. However, not all double merles are easily identifiable, and some may appear relatively normal at first glance.
Is it ethical to breed merle dogs?
The ethics of breeding merle dogs are often debated. While responsible breeders can produce healthy merle puppies by carefully selecting breeding pairs and avoiding merle-to-merle matings, there are concerns about perpetuating a gene that can cause severe health problems.
Can two non-merle dogs produce a merle puppy?
No, two dogs without the merle gene cannot produce a merle puppy. The merle gene is dominant, meaning that at least one parent must carry the gene for it to be expressed in the offspring. However, a cryptic merle may appear as a non-merle, but still carry the gene and pass it on.
What is “phantom merle”?
“Phantom merle” is an informal term used to describe a merle dog that doesn’t display the typical merle pattern. This can occur due to various factors, including modifier genes or the specific type of merle allele present. These dogs can still pass on the merle gene to their offspring.
How does white spotting affect the appearance of merle patterns?
White spotting (piebald or extreme white) can mask or alter the appearance of the merle pattern. Extensive white markings can cover up the diluted and non-diluted patches, making it difficult to discern the underlying merle.
What is the ideal coat care for a merle dog to maintain its vibrant color?
Proper coat care for a merle dog generally involves regular brushing to remove loose hair and prevent matting. High-quality dog food and occasional bathing with a color-enhancing shampoo can help maintain the vibrancy of the coat, especially for blue merle dogs. Avoid excessive sun exposure, as it can fade the coat color over time.