page_title: Dominant white
section_title: Allelic series
hierarchical_section_title: Dominant white / Inheritance / Allelic series
caption_attribution_description: English: Buchiko (Racehorse of Japan. Dominant white horse) 日本語: ブチコ（第22回チューリップ賞パドック）。投稿者が撮影および編集
context_page_description: Dominant white or white spotting is a group of genetically related coat color conditions in the horse, best known for producing an all-white coat, but also able to produce various forms of white spotting and white markings, several of which are sometimes referred to as sabino.
  There are many different forms of dominant white or white spotting; as of 2018 they are labeled W1 through W27 and are associated with the KIT gene, along with Sabino 1. The white spotting produced can range from flashy white markings like those made by W20, to patterns similar to Sabino 1, to a fully white or almost fully white horse. White horses are born with unpigmented pink skin and white hair, usually with dark eyes. Under normal conditions, at least one parent must be dominant white to produce dominant white offspring. However, most of the currently-known alleles of dominant white can be linked to a documented spontaneous mutation in a single ancestor. For many of the W alleles, the white coats are, as the name suggests, inherited dominantly, meaning that a horse only needs one copy of the allele to have a white or white spotted coat.
context_section_description: The KIT gene contains over 2000 base pairs, and a change in any of those base pairs results in a mutant allele. Over forty seven such alleles have been identified by sequencing the KIT genes of various horses. The resultant phenotype of many of these alleles is not yet known, but 29 have been linked to white spotting.  To date, DNA tests can identify if a horse carries the various identified W alleles, some commercially available.
  W1 is found in Franches Montagnes horses descended from a white mare named Cigale born in 1957. Cigale's parents' coats were not extensively marked. A single nucleotide polymorphism (SNP), a type of mutation in which a single nucleotide is accidentally exchanged for another, is thought to have occurred with Cigale. This mutation (c.2151C>G) is predicted to truncate the protein in the middle of the tyrosine kinase domain, which would severely affect the function of KIT. It is a nonsense mutation located on exon 15 of KIT.  Some horses with the W1 mutation are born pure white, but many have residual pigment along the topline, which they may then lose over time. Based on studies of KIT mutations in mice, the severity of this mutation suggests that it may be nonviable in the homozygous state. However, horses with the W1 mutation have been found to have normal blood parameters and do not suffer from anemia.
  W2 is found in Thoroughbred horses descended from KY Colonel, a stallion born in 1946. While KY Colonel was described as a chestnut with extensive white markings, he is known for siring a family of pure white horses through his white daughter, White Beauty, born in 1963. His son War Colors was registered as roan because he had some spots of color, but later became white. The W2 allele is linked to a single nucleotide polymorphism (c.1960G>A), a missense mutation where a glycine is replaced with arginine (p.G654R) in the protein kinase domain, located on exon 17.
  W3 is found in Arabian horses descended from R Khasper, a near-white stallion born in 1996. Neither of his parents were white, and the causative mutation (c.706A>T) is thought to have originated with this horse. It is a nonsense mutation on exon 4, predicted to truncate the protein in the extracellular domain. Horses with the W3 allele often retain interspersed flecks or regions of pigmented skin and hair, which may fade with time. Some members of this family possess blue eyes, but these are thought to be inherited separately from the white coat. Based on similar studies in mice, researchers have named W3 as potentially homozygous nonviable.
  W4 is found in Camarillo White Horses, a breed characterized by a white coat, beginning with a spontaneous white stallion born in 1912 named Sultan. Like W1 and W3, these horses may be pure white or near-white, with pigmented areas along the topline that fade with time. This mutation is an SNP (c.1805C>T) which produces a missense mutation replacing alanine with valine in the kinase domain, on exon 12.
  W5 is found in Thoroughbreds descending from Puchilingui, a 1984 stallion with sabino-like white spotting and roaning. Horses with the W5 allele exhibit a huge range in white phenotype: a few have been pure white or near-white, while others have sabino-like spotting limited to high, irregular stockings and blazes that covered the face. Twenty-two members of this family were studied, and the 12 with some degree of white spotting were found to have a deletion in exon 15 (p.T732QfsX9), in the form of a frameshift mutation. A later study found that the members of this family with the greatest depigmentation were compound heterozygotes who also carried the W20 allele.
  W6 is found in one near-white Thoroughbred named Marumatsu Live born to non-white parents in 2004. The potential range of expressivity, therefore, is not yet known. The mutation (c.856G>A) is thought to have occurred spontaneously in this horse.  It is a missense mutation on exon 5.
  W7 is found in another near-white Thoroughbred named Turf Club born in 2005 to a dam that had nine other offspring, all non-white.  The dam did not possess the W7 a
caption: This near-white mare is a daughter of Shirayukihime,[23] the suspected founder of the W14 mutation. Horses with W14 are often fully white.[21]
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