Unlike the other multi colored poodle patterns, merle is highly controversial. While parti, phantom, sable, and brindle dogs have been documented throughout the history of the breed, no one seems to know where the merle color came from. It almost certainly was introduced through cross breeding at some point in poodle history. But whether that cross happened in the beginning of breed development and should be considered as much a part of the poodle’s gene pool as the other multi colors or if it occurred more recently and should be considered proof of crossbreeding only a few generations back is unclear. The other multi colors are known to be caused by recessive genes, merle is caused by a dominant gene. While merle can be hidden by other genes (recessive red, greying, or a white masking gene, for example) it seems unlikely to be passed along unknowingly for hundreds of years before suddenly being rediscovered. Adding to the controversy, merle is well known to be associated with several health problems, some of them extremely severe.
Perhaps the most compelling argument for merle being a recent introduction to the poodle gene pool is that they majority of breeders who breed for this color seem to be involved in breeding practices that are, generally, considered less ethical by reputable breeders. A Google search for merle poodles turns up a lot of breeders specializing in “designer” mixes such as “aussie-doodles” and “cock-a-poos.”
Merle is a dilution gene, that is, it lightens whatever the coat color would otherwise have been by diluting eumelanin. Phaeomelanin (red) is not affected at all and will appear as normal. The lightening is not spread evenly over the coat, but leaves patches of undiluted color scattered over the dog’s body. One dose of the merle gene on an otherwise black dog produces a blue merle - a more or less bluish gray dog dappled with black spots. Merle acts on the black pigment in the iris of the eye just as it does on the coat, so merle dogs often have part or all of the eye blue.
On a double merle, both eumelanin and phaeomelanin pigments are affected. Double merles are typically mostly white and may have merle patches on the head and sometimes the body. Sometimes double merles are even born completely white. Some double merles are perfectly healthy, but eye defects and deafness (due to lack of pigment in parts of the inner ear) are extremely common, as well as sunburn and skin cancer on exposed pink areas. Dogs with two copies of the merle gene (homozygous merle or “double merle”) have an even higher chance of being born deaf. The deafness is caused by lack of pigment in the inner ear. The genes which determine white markings impact pigment cells wherever they occur in the body, not just in the coat. A tiny organ in the inner ear called a cochlea contains fluid and is lined with hair-like structures called cillia. When sound vibrates the air, those vibrations travel through the ear canal and vibrate the fluid which wiggles the cilia. The cilia connect with nerve endings through pigment cells. If the pigment cells are absent, this translation can’t take place and the dog will be deaf in that ear.
A double merle can only be bred from two merles, as it requires an M gene from each parent. As merle is dominant, no dogs can be carriers of it - any dog with one M gene will be a merle. However, occasionally merle can be hidden by other genes. A recessive red dog, for example, will not display any merle because it is unable to make eumelanin in its coat, and the merle gene only affects eumelanin. Merle can be very difficult to see on a brindle dog or a dog with the greying gene. Merle can also be hidden if the dog has very heavy markings, so a blue merle could appear completely black if the patches are large enough (a cryptic merle). Sometimes the hidden merles described above have a blue eye or a butterfly nose, which give away their merle gene, but often there is no sign at all that they are merle.
Unlike the other non-standard colors, merle is not the result of recessive genes hiding from the original outcrossing done to downsize the Standard Schnauzer. In fact, the introduction of the merle gene by crossing to other breeds (especially Australian Shepherds, Pomeranians, and Poodles) is well documented. The initial cross was made specifically to introduce the merle color into the Miniature Schnauzer gene pool, with subsequent generations using only these Schnauzer mixes and purebred Schnauzers. Some breed enthusiasts argue that a merle Schnauzer cannot be purebred due to the color, while proponents argue that after the fifth generation they breed true with essentially none of the traits from the original crossbreeding remaining. This is a striking pattern with a lot of controversy behind it due to the health problems associated with the merle gene.
Merle is a dilution gene, that is, it lightens whatever the coat color would otherwise have been by diluting eumelanin. Phaeomelanin (red) is not affected at all and will appear as normal. The lightening is not spread evenly over the coat, but leaves patches of undiluted color scattered over the dog’s body. One dose of the merle gene on an otherwise black dog produces a blue merle - a more or less bluish gray dog dappled with black spots. Merle acts on the black pigment in the iris of the eye just as it does on the coat, so merle dogs often have part or all of the eye blue.
On a double merle, both eumelanin and phaeomelanin pigments are affected. Double merles are typically mostly white and may have merle patches on the head and sometimes the body. Sometimes double merles are even born completely white. Some double merles are perfectly healthy, but eye defects and deafness (due to lack of pigment in parts of the inner ear) are extremely common, as well as sunburn and skin cancer on exposed pink areas. Dogs with two copies of the merle gene (homozygous merle or “double merle”) have an even higher chance of being born deaf. The deafness is caused by lack of pigment in the inner ear. The genes which determine white markings impact pigment cells wherever they occur in the body, not just in the coat. A tiny organ in the inner ear called a cochlea contains fluid and is lined with hair-like structures called cillia. When sound vibrates the air, those vibrations travel through the ear canal and vibrate the fluid which wiggles the cilia. The cilia connect with nerve endings through pigment cells. If the pigment cells are absent, this translation can’t take place and the dog will be deaf in that ear.
A double merle can only be bred from two merles, as it requires an M gene from each parent. As merle is dominant, no dogs can be carriers of it - any dog with one M gene will be a merle. However, occasionally merle can be hidden by other genes. A recessive red dog, for example, will not display any merle because it is unable to make eumelanin in its coat, and the merle gene only affects eumelanin. Merle can be very difficult to see on a brindle dog or a dog with the greying gene. Merle can also be hidden if the dog has very heavy markings, so a blue merle could appear completely black if the patches are large enough (a cryptic merle). Sometimes the hidden merles described above have a blue eye or a butterfly nose, which give away their merle gene, but often there is no sign at all that they are merle.
