Breeding programmes of American Paint and Quarter Horses relay strongly on genetic tests for genetic diseases and known genetic background of coat colour and pattern. Diluted colours which are caused by three loci, dun, cream and champagne, are very popular in breeding programmes. Although dun is a common phenotype in wild Equid species (zebras) it is rare in domestic horses and is present in only a few breeds. In addition to the functional D allele, there are two additional alleles, nondun 1 (nd1) and non-dun 2 (nd2). The D allele is dominant and is phenotypically expressed by a strong dark dorsal stripe, zebra markings on the legs, darker area around the muzzle (primitive markings), darker mane and tail and diluted coat colour. The nd1 allele or pseudo dun shows at the phenotypic level some characteristics of the dun phenotype, but with lower intensity, while the nd2 allele does not express primitive markings and diluted coat colour. The effect of alleles at the dun locus was shown by comparing the phenotype and genotype of 62 horses. We also made an expression analysis of the TBX3 (dun) gene at the RNA level for different mane samples of the horse with a complex phenotype. Dun dilution can be also found in combination with two other dilution genes, champagne and cream. When expressed together, they cause a more intense effect on the phenotype, which we presented with the help of photographs. Especially popular is the combination of functional alleles at the dun and champagne locusBreeding programmes of American Paint and Quarter Horses relay strongly on genetic tests for genetic diseases and known genetic background of coat colour and pattern. Diluted colours which are caused by three loci, dun, cream and champagne, are very popular in breeding programmes. Although dun is a common phenotype in wild Equid species (zebras) it is rare in domestic horses and is present in only a few breeds. In addition to the functional D allele, there are two additional alleles, nondun 1 (nd1) and non-dun 2 (nd2). The D allele is dominant and is phenotypically expressed by a strong dark dorsal stripe, zebra markings on the legs, darker area around the muzzle (primitive markings), darker mane and tail and diluted coat colour. The nd1 allele or pseudo dun shows at the phenotypic level some characteristics of the dun phenotype, but with lower intensity, while the nd2 allele does not express primitive markings and diluted coat colour. The effect of alleles at the dun locus was shown by comparing the phenotype and genotype of 62 horses. We also made an expression analysis of the TBX3 (dun) gene at the RNA level for different mane samples of the horse with a complex phenotype. Dun dilution can be also found in combination with two other dilution genes, champagne and cream. When expressed together, they cause a more intense effect on the phenotype, which we presented with the help of photographs. Especially popular is the combination of functional alleles at the dun and champagne locus.
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