Dominant White 15 (W15)
Gene or Region: KIT
Reference Variant: A (N)
Mutant Variant: G (W15)
Affected Breeds: Arabian
Research Confidence: High - Mutations in KIT have been well-documented to cause white spotting in both the horse and other species
Explanation of Results: W15/W15 = homozygous for Dominant White 15, white markings expressed W15/n = heterozygous for Dominant White 15, white markings expressed n/n = no variant detected
General Description for Dominant White 15
Dominant White 15 (W15) is found in Arabian horses and may result in either a partially or a completely white coat color.
W15 Founder: Khartoon Klassic (born 1996)
W15 Phenotype: Partially white (heterozygous), completely white (homozygous)
Gene Information
KIT is a tyrosine kinase receptor that is vital for normal development. Mutations in other species have led to white spotting, anemia, sterility, and certain types of tumors. However, no negative health effects associated with dominant white have ever been documented in the horse. The various W alleles encompass a variety of mutations, all resulting in changes to the encoded protein.
References
Haase B et al., “Allelic heterogeneity at the equine KIT locus in dominant white (W) horses.” (2007) PLoS Genet. 3: e195.
Haase B et al., “Seven novel KIT mutations in horses with white coat colour phenotypes.” (2009) Anim Genet. 40: 623-9.
Holl H et al., “De novo mutation of KIT discovered as a result of a non-hereditary white coat colour pattern.” (2010) Anim Genet. 41: 196-8.
Haase B et al., “Five novel KIT mutations in horses with white coat colour phenotypes.” (2011) Anim Genet. 42: 337-9.
Hauswirth R et al., “Novel variants in the KIT and PAX3 genes in horses with white-spotted coat colour phenotypes.” (2013) Anim Genet. 44: 763-5.
Holl H et al., “A novel splice mutation within equine KIT and the W15 allele in the homozygous state lead to all white coat color phenotypes.” (2017) Anim Genet. DOI: 10.1111/age.12554
Durig N et al., “Whole genome sequencing reveals a novel deletion variant in the KIT gene in horses with white spotted coat colour phenotypes.” (2017) Anim Genet. In press.
Photo of Khartoon Khlassic, courtesy of Marla Melloway.
More Horse Color Genetics
Dun / Non-Dun
Dun (D) is a dilution that affects both black and red pigment types. Two non-dun (nd1 & nd2) variants have been discovered, with nd1 being associated with primitive markings (such as a characteristic dorsal stripe) in non-dilute horses, and nd2 showing neither dilution nor primitive markings.