Horse Coat Color Research Articles

Seven novel KIT mutations in horses with white coat colour phenotypes

White coat colour in horses is inherited as a monogenic autosomal dominant trait showing a variable expression of coat depigmentation. Mutations in the KIT gene have previously been shown to cause white coat colour phenotypes in pigs, mice and humans. We recently also demonstrated that four independent mutations in the equine KIT gene are responsible for the dominant white coat colour phenotype in various horse breeds. We have now analysed additional horse families segregating for white coat colour phenotypes and report seven new KIT mutations in independent Thoroughbred, Icelandic Horse, German Holstein, Quarter Horse and South German Draft Horse families. In four of the seven families, only one single white horse, presumably representing the founder for each of the four respective mutations, was available for genotyping. The newly reported mutations comprise two frameshift mutations (c.1126_1129delGAAC; c.2193delG), two missense mutations (c.856G>A; c.1789G>A) and three splice site mutations (c.338-1G>C; c.2222-1G>A; c.2684+1G>A). White phenotypes in horses show a remarkable allelic heterogeneity. In fact, a higher number of alleles are molecularly characterized at the equine KIT gene than for any other known gene in livestock species.

Missense mutation in exon 2 of SLC36A1 responsible for champagne dilution in horses.

Champagne coat color in horses is controlled by a single, autosomal-dominant gene (CH). The phenotype produced by this gene is valued by many horse breeders, but can be difficult to distinguish from the effect produced by the Cream coat color dilution gene (CR). Three sires and their families segregating for CH were tested by genome scanning with microsatellite markers. The CH gene was mapped within a 6 cM region on horse chromosome 14 (LOD = 11.74 for θ = 0.00). Four candidate genes were identified within the region, namely SPARC [Secreted protein, acidic, cysteine-rich (osteonectin)], SLC36A1 (Solute Carrier 36 family A1), SLC36A2 (Solute Carrier 36 family A2), and SLC36A3 (Solute Carrier 36 family A3). SLC36A3 was not expressed in skin tissue and therefore not considered further. The other three genes were sequenced in homozygotes for CH and homozygotes for the absence of the dilution allele (ch). SLC36A1 had a nucleotide substitution in exon 2 for horses with the champagne phenotype, which resulted in a transition from a threonine amino acid to an arginine amino acid (T63R). The association of the single nucleotide polymorphism (SNP) with the champagne dilution phenotype was complete, as determined by the presence of the nucleotide variant among all 85 horses with the champagne dilution phenotype and its absence among all 97 horses without the champagne phenotype. This is the first description of a phenotype associated with the SLC36A1 gene.

Technical note: A novel method for routine genotyping of horse coat color gene polymorphisms1

The aim of this note is to describe a reliable, fast, and cost-effective real-time PCR method for routine genotyping of mutations responsible for most coat color variation in horses. The melanocortin-1 receptor, Agouti-signaling peptide, and membrane-associated transporter protein alleles were simultaneously determined using 2 PCR protocols. The assay described here is an alternative method for routine genotyping of a defined number of polymorphisms. Allelic variants are detected in real time and no post-PCR manipulations are required, therefore limiting costs and possible carryover contamination. Data can be copied to a Microsoft Excel spreadsheet for semiautomatic determination of the genotype using a macro freely available at http://www.igijon.com/personales/fgoyache/software_i.htm (last accessed February 26, 2007). The performance of the method is demonstrated on 156 Spanish Purebred horses.

Whole-genome linkage disequilibrium screening for complex traits in horses

The identification of candidate genes for significant traits is crucial. In this study, we developed and tested effective and systematic methods based on linkage disequilibrium (LD) for the identification of candidate regions for genes with Mendelian inheritance and those associated with complex traits. Our approach entailed the combination of primary screening using pooled DNA samples based on DeltaTAC, secondary screening using an individual typing method and tertiary screening using a permutation test based on the differences in the haplotype frequency between two neighbouring microsatellites. This series of methods was evaluated using horse coat colour traits (chestnut/non-chestnut) as a simple Mendelian inheritance model. In addition, the methods were evaluated using a complex trait model constructed by mixing samples from chestnut and non-chestnut horses. Using both models, the methods could detect the expected regions for the horse coat colour trait. The results revealed that LD extends up to several centimorgans in horses, indicating that whole-genome LD screening in horses could be performed systematically and efficiently by combining the above-mentioned methods. Since genetic maps based on microsatellites have been constructed for many other species, the approaches present here could have wide applicability.

Quantitative genetic aspects of coat color in horses1

The aim of this study was to estimate genetic parameters for coat color in horses. Besides defining coat color classes (gray, chestnut, bay, and black), the phenotypes were also measured quantitatively according to standardized international procedures (Commission Internationale de l'Eclairage L*, a*, b*), where L* describes lightness, a* describes color saturation from red to green, and b* describes color saturation from yellow to blue. The total color saturation was derived from a* and b* and referred to as Chroma. A total of 294 horses from the breeds Lipizzan, Nonius, Arabian Pure Bred, Shagya Arabian, and Gidran were measured at neck, shoulder, and belly. Heritabilities (within and between breeds or color classes) and repeatabilities were estimated using REML from univariate animal models defined separately for gray and nongray horses. For gray horses, the estimated within-breed heritabilities for L* ranged from 0.45 to 0.49 and for a*, b*, and Chroma from 0.09 to 0.52, indicating moderate polygenic effect. For nongray horses, between-color class heritabilities were high (0.70 to 0.85) and within-color class heritabilities were negligible (except for L* measured on neck and belly, 0.21 and 0.34, respectively). Additionally, the importance of L* was described by the relation with the total melanin content of horse coat hair; for gray and nongray horses, a strong negative linear relationship was detected (P < 0.01). The spectrometric measures and the results of this study demonstrate a possible approach to the estimation of the polygenic component involved in coat color inheritance.

Genetic Diversity of Hair Colour in Horses

The main aim of this study was to analyze sources of variability for coat colour expressed as a quantitative trait as well as to determine non genetic factors influencing horse colour variation and shades. Traditional Hungarian horse breeds such as Lipizzan (grey), Gidran (chestnut), Shagya Arabian and Arabian Pure Bred (grey) and Nonius (bay and black) horses were involved in the current study. We report results using direct measurements of horse coat colour using objective colorimetric dimensions and a spectrophotometer for determining hair melanin. Correlation analysis indicated that the single biological component that correlated best with the total melanin content of horse hair is the L* value (r=-0.858, p&lt;0.0001). Subjective colour classes and coat colour variables L* and a* were obviously related, with R2 values of 0.88 and 0.46 respectively, with a lower R2 for b* of 0.22 (all p&lt;0.001).

Melanocortin receptor variants with phenotypic effects in horse, pig, and chicken.

The melanocortin system is of considerable interest in domestic animals because their energy metabolism and pigmentation have been under strong selection. This article reviews our work on MC1R variants in horse, pig, and chicken, as well as a study on MC4R polymorphism in the pig. The chestnut coat color in horses is caused by an MC1R missense mutation (S83F). In the pig, we have described seven MC1R alleles controlling four different coat color phenotypes (wild type, dominant black, black spotting, and recessive red). The most interesting allele is the one causing black spotting because it carries two causative mutations, a frameshift and a missense mutation. The frameshift mutation is somatically unstable, and the black spots reflect somatic reversion events restoring the reading frame. Classic genetics have established eight alleles at the Extended black locus in chicken, which is assumed to correspond to the Extension locus in mammals. We have analyzed the co-segregation of alleles at MC1R and Extended black using a red jungle fowl x White Leghorn intercross and provide compelling evidence that these loci are identical. A previous study indicated that a missense mutation (D298N) in pig MC4R has an effect on fatness, growth, and feed intake. We could not confirm this association using an intercross between the wild boar and Large White domestic pigs, but it is possible that our F(2) generation was too small to detect the rather modest effect reported for this polymorphism.

Close association between sequence polymorphism in the KIT gene and the roan coat color in horses.

The roan coat color in horses is controlled by a dominant allele that is lethal in the homozygous condition. Phenotypic similarities to some pigmentation disorders in human and mouse, combined with comparative mapping data, identified KIT, encoding the mast cell growth factor receptor, as a major candidate gene for the roan locus (Rn). Rn has previously been mapped to equine linkage group (LG) II. In this study, LGII was expanded with KIT and PDGFRA (platelet-derived growth factor receptor alpha) by use of RFLP and linkage analysis. Moreover, highly significant linkage disequilibrium between Rn and a KIT TaqI RFLP, representing a synonymous substitution in exon 19, was revealed. There was a strong KIT-Rn association in most breeds. Almost the complete KIT-encoding sequence was determined by sequence analysis of RT-PCR products. Comparison of horse KIT cDNA sequences, representing three different alleles (two different rn and one Rn), revealed five sequence polymorphisms and several mRNA splice variants, but none of these proved to be specifically associated with Rn. An insertion of a partial (79 bp) LINE1-element between exons 1 and 2, leading to a frameshift, represented about 30% of KIT transcripts in the Belgian roan horse used for the sequence analysis. However, an association between this L1 splice insertion and the roan phenotype was not verified when testing additional unrelated roan and non-roan horses from different breeds. The study strengthens the hypothesis that the roan coat color is controlled by KIT, but further analyses are needed to reveal the causative mutation(s).

A missense mutation in the gene for melanocyte-stimulating hormone receptor (MC1R) is associated with the chestnut coat color in horses.

The melanocyte-stimulating hormone receptor gene (MC1R) is the major candidate gene for the chestnut coat color in horses since it is assumed to be controlled by an allele at the extension locus. MC1R sequences were PCR amplified from chestnut (e/e) and non-chestnut (E/-) horses. A single-strand conformation polymorphism was found that showed a complete association to the chestnut coat color among 144 horses representing 12 breeds. Sequence analysis revealed a single missense mutation (83Ser-->Phe) in the MC1R allele associated with the chestnut color. The substitution occurs in the second transmembrane region, which apparently plays a key role in the molecule since substitutions associated with coat color variants in mice and cattle as well as red hair and fair skin in humans are found in this part of the molecule. We propose that the now reported mutation is likely to be the causative mutation for the chestnut coat color. The polymorphism can be detected with a simple PCR-RFLP test, since the mutation creates a TaqI restriction site in the chestnut allele.

Behavioural testing of dogs in animal shelters to predict problem behaviour

Mutations in the genes influencing melanocytes not only affect the colour of an animal, but are also believed to impact physiological and behavioural functions. When this is taken into consideration, the common perception among horse owners that the chestnut coat colour is associated with adverse behaviours seems plausible. The aim of this study was to explore this perception by providing insight into any potential genetic associations between coat colour and adverse behaviours in horses. Data were acquired through an internationally accessible online questionnaire. Respondents provided information on their horse's behaviour during general handling, whilst being exercised, towards different stimuli in their environment and when isolated from other horses. Analyses considered behavioural data on 477 horses that represented a range of breeds, ages, and event disciplines. The breed, sex, and age of the horse significantly (P < 0.05) influenced many of the equine behaviours assessed in the questionnaire. Significant differences in behavioural responses between bay and chestnut horses were only present for four questions. No evidence was found to support that chestnut horses are more likely than bay horses to display behaviours often associated with training difficulties. However, chestnut horses were more likely to approach objects and animals in their environment, regardless of their familiarity. This suggests that selection for the chestnut phenotype in horses may have inadvertently involved selection for boldness and altered the way horses interact with their surroundings.

A new scheme for describing horse coat colour

A new descriptive scheme of horse colours is proposed with four dimensions: (1) pigmentary pattern (which deals with the symmetric partition of eumelanic — black or brown — and phaeomelanic — red — pigmented areas (five different types)); (2) eumelanic type (black or brown); (3) pigment alteration (a modification of pigmentary appearance inside the hair or an intermixing of white and pigmented fibres); and (4) white designs (when the white patches are clearly distinct from the coloured ones). The advantage of this new descriptive scheme are: (1) a better connection with the biological and genetic realities; (2) a more accurate description of the very numerous different colour phenotypes: and (3) a more assimilable international language.

A new interpretation of the inheritance of the horse colors dun and Isabella in a Russian stud during the period 1854–1894

A new interpretation of the inheritance of the horse colors dun and Isabella in a Russian stud during the period 1854–1894

Confirmation of a gene for dominant dilution of horse colors

Confirmation of a gene for dominant dilution of horse colors

A allele necessary for dilute coat color in horses.

A allele necessary for dilute coat color in horses.

THE GENETICS OF COAT COLOR IN HORSES

Journal Article THE GENETICS OF COAT COLOR IN HORSES Get access W. E. CASTLE W. E. CASTLE Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Heredity, Volume 31, Issue 3, March 1940, Pages 127–128, https://doi.org/10.1093/oxfordjournals.jhered.a104856 Published: 01 March 1940

The colours of horses

The colours of horses

The colours of horses

The colours of horses

The colours of horses

Journal Article The colours of horses Get access George Watson Cole George Watson Cole Search for other works by this author on: Oxford Academic Google Scholar Notes and Queries, Volume s2-IX, Issue 237, 28 October 1922, Page 357, https://doi.org/10.1093/nq/s2-IX.237.357f Published: 28 October 1922

The colours of horses

The colours of horses Get access Herbert Maxwell Herbert Maxwell 1Monreith Search for other works by this author on: Oxford Academic Google Scholar Notes and Queries, Volume s12-XI, Issue 230, 9 September 1922, Page 212, https://doi.org/10.1093/nq/s12-XI.230.212b Published: 09 September 1922

The colours of horses

The colours of horses