S Locus (S-LOCUS)
A mutation in the MITF gene is responsible for the disruption of pigment production which results in white or non-pigmented areas within a dog’s coat. The white coat coloration that results from this mutation can be observed in a number of different patterns that are often referred to as piebald, particolor, extreme white, landseer, flowered or Blenheim. Dogs that carry one copy of the mutation will typically show limited white spotting across their coat while dogs that carry two copies of the mutation will have nearly solid white coats with limited or no spots of additional coloring. It is important to note that the S Locus mutation will not identify a pattern of white spotting known as “Irish White Spotting” which is due to another unknown mutation.
A (CLEAR/NORMAL): These dogs have two copies of the normal gene and will have no white spotting, parti, piebald or flash coat color.
B (CARRIER/AFFECTED): These dogs have one copy of the normal gene and one copy of the mutation associated with white coat color. They will have limited white spotting, flash, parti, or piebald coat color and, if bred, will pass the mutation to 50% of its offspring, on average.
C (AT RISK/AFFECTED): These dogs have two copies of the mutation associated with white coat color which results in a nearly solid white, parti, or piebald coat color.