S Locus (White Spotting, Parti, or Piebald)
The S Locus (White spotting) coat colour test reliably determines if a dog has one of the following genotypes at the S locus:
|S/S||This dog carries two copies of S which results in a solid coat with no white spotting, flash, parti, or piebald coat colour. This dog will pass on one copy of S to 100% of its offspring.Interpretation: No white spotting, flash, parti, or piebald|
|S/sp||This dog carries one copy of S and one copy of sp which results in limited white spotting, flash, parti, or piebald coat colour due to the co-dominance of S and sp. This dog will pass on one copy of S to 50% of its offspring and one copy of sp to 50% of its offspring.Interpretation: Limited white spotting, flash, parti, or piebald (Carrier)|
|sp/sp||This dog carries two copies of sp which results in a nearly solid white parti, or piebald coat colour. This dog will pass on one copy of spto 100% of its offspring.Interpretation: Nearly solid white, parti, or piebald|
The MITF gene, also known as the S Locus, is a master regulator that controls pigmentation. An insertion in the MITF gene disrupts all pigment production resulting in non-pigmented areas with white coat colour and pink skin. However, the S and sp variants show co-dominant expression in some breeds when both are present (S/sp), resulting in limited white spotting due to limited expression from each variant. Although there are several other types of white spotting patterns, such as Irish white spotting (si), the DNA variations that cause these patterns are not known.
Genetic testing of the MITF gene will determine whether a dog is a genetic Carrier of white spotting coat colour. Dogs with an S/S coat colour genotype will have no white spotting, flash, parti, or piebald coat colour while dogs with an S/sp genotype will have limited white spotting, flash, parti, or piebald coat colour. Dogs with sp/sp genotypes will have a nearly solid white, parti, or piebald coat colour.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
- Karlsson EK, Baranowska I, Wade CM, Salmon Hillbertz NH, Zody MC, Anderson N, Biagi TM, Patterson N, Pielberg GR, Kulbokas EJ 3rd, Comstock KE, Keller ET, Mesirov JP, von Euler H, Kampe O, Hedhammar A, Lander ES, Andersson G, Andersson L, Londblad-Toh K. Efficient mapping of mendelian traits in dogs through genome-wide association. Nat Genet. 2007 Nov; 39(11):1321-8. [PubMed: 17906626]