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White spotting patterns that occur in many dog breeds do not have a uniform genetic basis. Some white patterns, such as the Irish spotting, are symmetrical with white markings on the undersides, collar and muzzle, and/or blaze such as seen in Boston Terriers and Corgis. The white pattern called mantle is phenotypically similar to Irish spotting but with more white extending onto the thigh and up the torso, as seen in some Great Danes. A pattern of less symmetrical white spotting, often called piebald, parti or random white, is present in many breeds. A DNA variant has been found in Microphthalmia Associated Transcription Factor- (MITF) gene that is associated with piebald spotting in many breeds.
The genetic determination of white spotting in dogs is complex. In breeds such as Collie, Great Dane, Italian Greyhound, Shetland Sheepdog, Boxer and Bull Terrier, piebald behaves as a dosage-dependent trait. A dog with one copy of the MITF variant has some white pattern expression, while a dog with 2 copies of the variant display more extreme white with color only on the head and perhaps a body spot. In Boxers and Bull Terriers, dogs with 2 copies of the MITF variant are completely white and dogs with 1 copy display the mantle (called flash in these breeds) pattern. However, additional mutations in MITF or other white-spotting genes appear to be present in these breeds that affect the amount of white being expressed. In other breeds, piebald behaves as a recessive trait- that is 2 copies of piebald are needed to produce white spotting.
The VGL is offering a test for piebald spotting to assist breeders with selection of matings that can produce the desired outcome for white. Breeds of interest for this test include:
Results are reported as:
N/N Dog has no copies of piebald
S/N Dog has 1 copy of piebald
S/S Dog has 2 copies of piebald
Note- expression of white patterns varies from breed to breed and among individuals within a breed. This test is specific for the mutation in MITF known to be associated with piebald/random white spotting.
Karlsson EK et al. Efficient mapping of mendelian traits in dogs through genome-wide association. Nature Genetics 2007, 39(11):1321-1328.
Schmutz S, TG Berryere and DL Dreger. MITF and white spotting in dogs: a population study. Journal of Heredity 2009, 100(Supl 1):S66-S74.