Decoding Coat Color Modifiers: White Spotting, Roaning, Saddle Tan, and Merle

Coat Color Modifiers

A number of genes are known to affect coat color in dogs. It is important to note that in some cases a dog’s  genetic and environmental factors may also influence color and pattern. Research on coat color and its modifiers is ongoing. In reference to the infographic above, take a look at four coat color modifiers that have been identified in dogs. 

White Spotting is primarily caused by a variant of the MITF gene. The genotype Ssp or spsp leads to a spotted phenotype. Dogs with one copy of the sp allele will likely have limited white spotting that is breed-dependent; while dogs with two copies will likely have breed-dependent white pattering, with a nearly white, parti, or piebald coat. The S locus, responsible for white spotting, does not explain all white spotting patterns in dogs, and other causes are currently being researched. The phenotype of white spotting can be seen in English Springer Spaniels, Cavalier King Charles Spaniels, and Landseer Newfoundlands, which are piebald. 

Roaning is strongly associated with a duplication in a region of the USH2A gene. Dogs with the genotypes Rr or RR may be roan. The roan allele (R) only impacts white which occurs as a result of the S locus. Dogs with at least one copy of R will likely have roaning on otherwise uniformly unpigmented white areas created by the sp allele at the S locus. Roaning can appear with or without ticking. The roan phenotype can be seen on Australian Cattle Dogs, English Setters, German Shorthaired Pointers, and English Cocker Spaniels among others. 

Saddle Tan is caused by a variant of the RALY gene that leads to select black hairs receding into a “saddle” shape on the back as the dog ages, leaving a tan face, legs, and belly. Dogs with one or two copies of the normal N allele (genotypes, NI or NN) are likely to have a saddle tan pattern. The RALY gene only impacts dogs that are kyky at the K locus, are atat or ata at the A locus, and are not ee at the E locus. The Saddle Tan phenotype can be seen on German Shepherd Dogs, Airedale Terriers, and Basset Hounds

Merle is determined by an insertion in the PMEL gene which is responsible for the mottled or patchy coat color of some dogs. Dogs with an M*m Embark test result are likely to have merle coat patterning or be “phantom” merle (where the merle pattern allele is not obvious in their coat). Dogs with an M*M* test result are likely to have merle or double merle coat patterning. The merle phenotype and the health concerns of having two merle alleles depends on the tail length of the SINE (Short Interspersed Element) Insertion. Learn more about tail length testing. The merle phenotype can be seen on Australian Shepherds, Border Collies, Collies, and Shetland Sheepdogs.

An expanded understanding of the genetic basis of coat colors may lead to new DNA tests for coat color. While it’s exciting for breeders to be able to test for traits when making breeding decisions, it is also important for breeders to be cognizant of any health risks that might be associated with certain traits. Responsible breeders use all the tools at their disposal from breed knowledge to comprehensive genetic testing and COI to produce healthy, happy puppies. 

 

 

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