The American Paint Horse Association (APHA) records pedigree and performance information for their breed, a stock‐type horse valued as a working farm or ranch horse and as a pleasure horse. As the name implies, the breed is also valued for its attractive white‐spotting patterns on the coat. The APHA utilizes visual inspections of photographs to determine if coat spotting exceeds threshold anatomical landmarks considered characteristic of desirable patterns. Horses with sufficient white patterning enter the ‘Regular’ registry, rather than the ‘Solid Paint‐Bred’ division, providing a threshold modeled phenotype. Genetic studies previously defined sequence variants corresponding to 35 alleles for white spotting in the horse. Here, we calculate the allele frequencies for nine common white‐spotting alleles in the American Paint Horse using a sample of 1054 registered animals. The APHA spotting phenotype is altered by additive interactions among spotting loci, and epistatically by the MC1R and ASIP genes controlling pigment production. The W20 allele within the KIT gene, independent of other known spotting alleles, was strongly associated with the APHA‐defined white‐spotting phenotype (P = 1.86 × 10⁻¹⁸), refuting reports that W20 acts only as a modifier of other underlying white‐spotting patterns. The parentage of an individual horse, either American Paint or American Quarter Horse, did not alter the likelihood of its entering the APHA Regular Registry. An empirical definition of the action of these genetic loci on the APHA‐defined white‐spotting phenotype will allow more accurate application of genome‐assisted selection for improving color production and the marketability of APHA horses.

中文翻译：

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包括W20在内的白色斑点等位基因对American Paint Horse中表型的影响。

美国漆马协会（APHA）记录了该品种的血统书和性能信息，这是一匹存栏型马，被视为农场，牧场和休闲马。顾名思义，该品种还因其在外套上具有吸引人的白色斑点图案而受到重视。APHA利用照片的视觉检查来确定涂层斑点是否超过认为是所需图案特征的阈值解剖学界标。具有足够白色图案的马匹进入“ Regular”注册表，而不是“ Solid Paint-Bred”分区，从而提供阈值建模表型。遗传研究先前定义了对应于35个等位基因的序列变体，用于在马中进行白点。这里，我们使用1054个注册动物的样本计算了美国漆马中9个常见的白色斑点等位基因的等位基因频率。APHA点样表型通过点样位点之间的加性相互作用而改变，并且通过MC1R和ASIP基因控制着色素的产生。KIT基因中的W20等位基因独立于其他已知的斑点等位基因，与APHA定义的白色斑点表型密切相关（P  = 1.86×10 ^-18），驳斥了有关W20的报道仅充当其他基础白点图案的修改器。一匹马（美国漆器或美国季马）的血统并没有改变其进入APHA常规注册表的可能性。这些遗传基因座对APHA定义的白点表型的作用的经验定义将允许更准确地应用基因组辅助选择，以改善颜色产生和APHA马的适销性。