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 c andidate gene for the chestnut coat color in horses since it is assume d 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 com plete association to the chestnut coat color among 144 horses represen ting 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 app arently plays a key role in the molecule since substitutions associate d 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 si te in the chestnut allele.