The merle gene has a unique affect on the Collie coat.
The merle gene is a dilution gene. It is not really a separate 'color', but genetic coding that dilutes color in the coat colors sable and tricolor. The pattern is irregular and patchy, with darker (normal) colors on a diluted base. The diluted base color is the work of the merle gene being present in that area, with the darker color being unaffected by the merle gene.
The merle gene always dilutes or lightens the sable and tricolor genes when present, creating the sable merle coat when present in Sable Collies and the blue merle coat when present in Tricolor Collies. The merle pattern is not a specific spotted pattern, but patchy and scattered over the body of the dog. The patches may be large or small. There may be few or many patches of merle in the coat.
There are also two other merle Collies: the Cryptic Merle and the Double Merle, also called a double dilute or white merle. The Cryptic Merle will have very little or no discernible merle patterns in the coat and appear to be a non-merle tricolor or sable. Most Cryptic Merles will have some evidence of the merle pattern somewhere on their bodies.
Merle Collies will have normal tan points and normal white accents, as any other Collie color. The merle gene does not affect either of these, only the coat color on the head and body.
Merle genes may affect one or both eyes, causing dark eyes to be blue, or flecked with blue. Blue eye color and flecking are acceptable in the Blue Merle Collie, though is not acceptable in the Sable Merle Collie**. Sable Merle is a normal color in Collies, just as is sable, tricolor, white and blue merle.
The merle gene may alter the color of the eyes, pads of the feet, and sometimes the nose, depending on where the merle pattern appears on the dog's body. Patches of diluted color can appear on any of these body parts if the merle gene is expressed in that area, where it is not expressed the color is the same as any sable or tricolor.
**The Collie Club of America defines what is acceptable in the AKC show ring, and the CCA Standard does not specifically mention the Sable Merle. It does state that the eyes of a Collie must be dark and matching in color, except for the Blue Merle. The Sable Merle Collie with blue eyes is penalized in the show ring. There are people who feel strongly on each side of this issue. Sable Merles with dark eyes have attained their championship titles when they have dark eyes, and because the merle pattern is usually gone by adulthood. There are many Collie Club of America member who are working to change the CCA Standard to include this color, since it is a normally occurring color in the breed, just as the blue merle color is. I would like to see the CCA include the Sable Merle Collie in the Standard, just as all the other naturally occurring colors are.
A Double Merle dog (two merle genes present) may have visual and hearing defects, including blindness, no hearing or both. It is suspected that some may have other internal health issues, some may have Microphthalmia or complete absence of the eye and underdeveloped hearing. A merle dog with color around the eyes and ears will usually have normal sight and hearing. A dog with no color (white merle) around the eyes and ears, may not have sight or hearing. There may be no defects in some dogs. The degree of defect depends on the degree of merle present in the eye and ear areas. This is why merle to merle breedings are not common. Double Merles cannot be shown in conformation classes.
Breeders avoid breeding two merle dogs because of the chance of defective puppies, though they can live a normal life with proper care. There are many internet groups that address living with and caring for deaf and blind dogs. Deaf dogs compete successfully in performance classes, can be therapy dogs, and live happy lives with their families. These groups would be excellent resources for those who are considering owning a deaf or blind dog.
Merle to Merle breedings will produce litters with:
1/4 Normally colored puppies (Tricolor &/or Sable - mm = no merle gene present) 1/4 Merle puppies (Blue Merle &/or Sable Merle - Mm = one merle gene present) 1/2 Double Merles (MM = two merle genes present) (Usually have defective vision and/or hearing)
Merle to Non-merle breedings will produce litters with:
1/2 Normally colored puppies (Tricolor &/or Sable - mm = no merle gene present) 1/2 Merle puppies (Blue Merle &/or Sable Merle - Mm = one gene present) Zero Double Merle puppies produced because two merle genes, one from each parent, must be present.
One dog we know (a 'white' Boxer) cannot hear and his owner uses vibration to get his attention. His owner thumps the floor or ground and his dog comes to that signal, as well as many hand & body signals. It is actually very simple to train a dog with non-verbal cues. Most "Hollywood" dogs are trained with non-verbal and verbal signals. I have to add that this deaf dog, is super attentive, and pays attention to his owner's every move. He is a confident, friendly and bold dog, and he has no idea that he has any kind of handicap. Outsiders never realize he cannot hear. I am not sure who is more wonderful...the dog or his owner. I don't believe a 'white' Boxer is affected by the merle gene, but by other genes causing a white coat. White in Boxers is not desirable because of the defects that can affect the dog. I used this Boxer as an example of a deaf dog who lives a normal and happy life, and I see how happy & content this dog is. Of course, we don't want to purposefully breed defective dogs.
Other breeds that have the merle gene: Many are herding breeds: Collies, Border Collies, Chihuahuas. Pembroke and Cardigan Welsh Corgis, Dachshunds, Louisiana Catahoula Leopard Dogs, Papillons and Australian Shepherds.
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