S-Locus

White spotting patterns occur in many dog breeds. The genetic determination of white spotting in dogs is complex and it has been found that is associated with Microphthalmia Associated Transcription Factor gene (MITF). Short interspersed nucleotide element (SINE) is responsible if the dog is spotted or not.

All dogs that are homozygous for the SINE insertion (genotype sp/sp) have white markings that cover either ventral surface (mantle pattern) or most of the body (piebald or extreme white spotting). Expression of white patterns varies from breed to breed and among individuals within a breed.

In most breeds, dogs heterozygous for the SINE insertion (genotype S/sp) are solid colour or have minimal white, such as on the toes. In some breeds, heterozygotes have white undersides, often with a white collar- the pattern is called pseudo-Irish.

All dogs without SINE insertion (genotype S/S) are solid or single-coloured.

This test is specific for the SINE mutation in MITF gene known to be associated with random white spotting - piebald. For testing of Irish spotting, a symmetrical white marking, this test is not appropriate.

Inheritance: autosomal co-dominant

Mutation: MITF gene