New Test: Color Locus S (Piebald or Extreme White Spotting)

Domestic dogs have great diversity in white spotting patterns ranging from extreme white to minimal white or completely solid color. The amount of white color is determined by genetic factors as well as by stochastic events in pigment cell development. It is important to understand that white color in domestic dogs is controlled by many variants as well as random events in the maturation of the cells.

The color and pattern of a dog's coat depend on the combined effects of many different genetic factors. Extreme white or white spotting is typically caused by combined and cumulative effects of multiple variants in MITF locus, and possibly in some other loci. A SINE insertion is often associated with extreme white and piebald spotting in some breeds.

  • Dogs homozygous for the SINE insertion (sp/sp; INS/INS) are usually white with minimal color on the head, or spotted.
  • In some breeds heterozygous dogs (S/sp; +/INS) have white collar around the neck and white undersides, which is called pseudo-irish spotting (to be distinguished from true irish spotting in which SINE insertion is absent). 
  • Dogs that do not carry the SINE (S/S; +/+) have usually solid color or very minimal white on toes or on the tip of the tail.