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Animal genetics2020; 51(5); 707-715; doi: 10.1111/age.12960

Impact of white-spotting alleles, including W20, on phenotype in the American Paint Horse.

Abstract: 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 ), 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.
© 2020 Stichting International Foundation for Animal Genetics.
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Publication Date: 2020-07-20 PubMed ID: 32686191DOI: 10.1111/age.12960Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research article discusses the effect of white-spotting alleles, in particular the W20 allele, on the phenotype of the American Paint Horse. The researchers studied the frequencies of nine common white-spotting alleles on a sample of 1054 registered horses and found that the spotting phenotype is influenced by the interactions among these genes, as well as the genes controlling pigment production. They also discovered that the presence of the W20 allele is strongly associated with a white-spotting phenotype, regardless of other spotting patterns.

Understanding American Paint Horse Breeding

  • The American Paint Horse Association (APHA) keeps records of pedigree and performance for this breed. These animals are popular farm or ranch horses and are also coveted for their striking white-spotting patterns.
  • The breed’s desirability is partly attributed to its coat patterning. The APHA uses visual inspections of pictures to determine whether a horse’s coat spotting exceeds certain anatomical landmarks considered characteristic of desirable patterns.
  • Horses with symmetrical white patterning are registered in the ‘Regular’ registry, while animals with less white patterning are categorized under the ‘Solid Paint-Bred’ division.

Frequency of White-Spotting Alleles

  • The study analyzed and calculated the frequency of nine prominent white-spotting alleles in the breed using a representative sample of 1054 registered American Paint Horses.
  • Previous scientific studies established 35 alleles for equine white spotting. Still, this paper focuses on the nine most common and how they present in this breed.

Impact of Genetic Interactions on Spotting Phenotype

  • A key finding of this research paper is that the spotting phenotype observed in Paint Horses is influenced not only by the interaction among these various spotting alleles but also by two genes controlling pigment production, namely MC1R and ASIP.
  • This additive and epistatic interaction leads to the variance in coat coloring and patterning observed within the breed.

The Role of the W20 Allele

  • Another significant finding is the influence of the W20 allele within the KIT gene. This study discovered a strong association between the presence of the W20 allele and the APHA-defined white-spotting phenotype.
  • Importantly, this finding challenges previous reports suggesting that W20 only acted as a modifier of other underlying white-spotting patterns. Instead, the presence of W20 alone seems to be a strong determinant of white spotting.

Implications for Horse Registry and Breeding Strategy

  • The research also found that a horse’s parentage, whether American Paint or American Quarter Horse, did not affect the chance of it being registered in the APHA Regular Registry, i.e., having sufficient white patterning.
  • Understanding the interplay of these genetic factors on coat spotting can allow for more accurate genome-assisted selection. This could improve color production and boost the breed’s marketability.

Cite This Article

APA
Brooks SA, Palermo KM, Kahn A, Hein J. (2020). Impact of white-spotting alleles, including W20, on phenotype in the American Paint Horse. Anim Genet, 51(5), 707-715. https://doi.org/10.1111/age.12960

Publication

Animal genetics
ISSN: 1365-2052
NlmUniqueID: 8605704
Country: England
Language: English
Volume: 51
Issue: 5
Pages: 707-715

Researcher Affiliations

Brooks, S A
  • Department of Animal Sciences, UF Genetics Institute, University of Florida, Gainesville, FL, 32611-0910, USA.
Palermo, K M
  • Department of Animal Sciences, UF Genetics Institute, University of Florida, Gainesville, FL, 32611-0910, USA.
Kahn, A
  • Department of Animal Sciences, UF Genetics Institute, University of Florida, Gainesville, FL, 32611-0910, USA.
Hein, J
  • American Paint Horse Association, Fort Worth, TX, 76161-0023, USA.

MeSH Terms

  • Alleles
  • Animals
  • Female
  • Gene Frequency / physiology
  • Hair Color / genetics
  • Horses / genetics
  • Horses / physiology
  • Male
  • Phenotype

Grant Funding

  • American Paint Horse Association

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Citations

This article has been cited 7 times.
  1. Avila F, Hughes SS, Magdesian KG, Penedo MCT, Bellone RR. Breed Distribution and Allele Frequencies of Base Coat Color, Dilution, and White Patterning Variants across 28 Horse Breeds. Genes (Basel) 2022 Sep 13;13(9).
    doi: 10.3390/genes13091641pubmed: 36140807google scholar: lookup
  2. Patterson Rosa L, Martin K, Vierra M, Lundquist E, Foster G, Brooks SA, Lafayette C. A KIT Variant Associated with Increased White Spotting Epistatic to MC1R Genotype in Horses (Equus caballus). Animals (Basel) 2022 Aug 2;12(15).
    doi: 10.3390/ani12151958pubmed: 35953947google scholar: lookup
  3. Hernández-Quiroz F, Murugesan S, Flores-Rivas C, Piña-Escobedo A, Juárez-Hernández JI, García-Espitia M, Chávez-Carbajal A, Nirmalkar K, García-Mena J. A high-throughput DNA sequencing study of fecal bacteria of seven Mexican horse breeds. Arch Microbiol 2022 Jun 10;204(7):382.
    doi: 10.1007/s00203-022-03009-2pubmed: 35687150google scholar: lookup
  4. Encina A, Sánchez-Guerrero MJ, Ligero M, Rodríguez-Sainz de Los Terreros A, Valera M. The Role of Genetic and Environmental Factors in White Leg Markings: Prevalence and Heritability Analysis in Pura Raza Española Horses. Life (Basel) 2025 Oct 23;15(11).
    doi: 10.3390/life15111661pubmed: 41302086google scholar: lookup
  5. Obradovic NA, McFadden A, Martin K, Vierra M, McLoone K, Martin E, Thomas A, Everts RE, Brooks SA, Lafayette C. Three Novel KIT Polymorphisms Found in Horses with White Coat Color Phenotypes. Animals (Basel) 2025 Mar 22;15(7).
    doi: 10.3390/ani15070915pubmed: 40218308google scholar: lookup
  6. Gossett CL, Guyer D, Hein J, Brooks SA. Digital Phenotyping Reveals Phenotype Diversity and Epistasis among White Spotting Alleles in the American Paint Horse. Genes (Basel) 2023 Oct 27;14(11).
    doi: 10.3390/genes14112011pubmed: 38002953google scholar: lookup
  7. Abondio P, Cilli E, Luiselli D. Human Pangenomics: Promises and Challenges of a Distributed Genomic Reference. Life (Basel) 2023 Jun 9;13(6).
    doi: 10.3390/life13061360pubmed: 37374141google scholar: lookup
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