Accumulating mutations in series of haplotypes at the KIT and MITF loci are major determinants of white markings in Franches-Montagnes horses.
Authors: Haase Bianca, Signer-Hasler Heidi, Binns Matthew M, Obexer-Ruff Gabriela, Hauswirth Regula, Bellone Rebecca R, Burger Dominik, Rieder Stefan, Wade Claire M, Leeb Tosso
Journal: PloS one
Summary
# Editorial Summary: White Markings in Franches-Montagnes Horses—A Complex Genetic Picture White facial and leg markings in horses represent a polygenic trait rather than the simple inheritance pattern seen in many other coat colour variants, yet their underlying genetics have remained poorly characterised until now. Researchers conducted a genome-wide association study in 1,077 Franches-Montagnes horses with standardised scoring of white patterning across the face and legs, identifying seven significant quantitative trait loci that collectively explain 54% of genetic variance in marking extent. The KIT and MITF loci emerged as the dominant contributors, accounting for 26% of this variance, with fine mapping revealing that mutations accumulate additively across haplotype variants at these loci to progressively increase white coverage—rather than producing threshold effects. The influence of both genes varies depending on the horse's base coat colour and the specific anatomical location of markings, suggesting complex interactions between these major loci and other genomic regions. For equine professionals involved in breeding programmes, pedigree analysis or advising clients on coat colour inheritance, this work demonstrates that white marking expression cannot be reliably predicted from simple genetic models, and that mare and stallion combinations should be assessed with consideration of both their individual genotypes at KIT and MITF and the cumulative mutation load these represent.
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Practical Takeaways
- •White marking patterns in horses are controlled by multiple genes (not single trait inheritance), with KIT and MITF being primary drivers but explaining less than half of variation
- •Breeders should understand that white marking extent involves additive genetic effects at multiple loci, making precise prediction difficult despite identified major genes
- •Coat color genetics interact with location and basic color, so similar genetic backgrounds may produce different marking patterns depending on these modifying factors
Key Findings
- •GWAS identified 7 quantitative trait loci affecting white marking score, with KIT, MITF, and MC1R as major loci
- •MITF and KIT together account for 26% of genetic variance in white marking score; all 7 loci explain 54%
- •KIT and MITF act additively with accumulating mutations progressively increasing extent of white markings
- •Influence of MITF and KIT varies by basic coat color and specific body location of white patterning