S-locus (piebald, white spotting)

White spotting in dogs is mostly caused by variations of MITF. Depending on a short interspersed nucleotide element (SINE), the dog is spotted or not. Del is the dominant allele and causes solid or single-coloured dogs (genotype del/del). Dogs that inherit SINE (genotype int/int) homozygous have white markings that either cover at least the ventral surface (mantle pattern) or most of the body (piebald or extreme white spotting). In most breeds, dogs heterozygous for the SINE-insertion (genotype del/int) are solid colored or have minimal white spots, e.g. on the toes. In some other breeds heterozygotes show white undersides, often with a white collar called pseudo-Irish.