Mutations in the agouti (ASIP), the extension (MC1R), and the brown (TYRP1) loci and their association to coat color phenotypes in horses (Equus caballus)

Mamm Genome. 2001 Jun;12(6):450-5. doi: 10.1007/s003350020017.


Coat color genetics, when successfully adapted and applied to different mammalian species, provides a good demonstration of the powerful concept of comparative genetics. Using cross-species techniques, we have cloned, sequenced, and characterized equine melanocortin-1-receptor (MC1R) and agouti-signaling-protein (ASIP), and completed a partial sequence of tyrosinase-related protein 1 (TYRP1). The coding sequences and parts of the flanking regions of those genes were systematically analyzed in 40 horses and mutations typed in a total of 120 horses. Our panel represented 22 different horse breeds, including 11 different coat colors of Equus caballus. The comparison of a 1721-bp genomic fragment of MC1R among the 11 coat color phenotypes revealed no sequence difference apart from the known chestnut allele (C901T). In particular, no dominant black (ED) mutation was found. In a 4994-bp genomic fragment covering the three putative exons, two introns and parts of the 5'- and 3'-UTRs of ASIP, two intronic base substitutions (SNP-A845G and C2374A), a point mutation in the 3'-UTRs (A4734G), and an 11-bp deletion in exon 2 (ADEx2) were detected. The deletion was found to be homozygous and completely associated with horse recessive black coat color (Aa/Aa) in 24 black horses out of 9 different breeds from our panel. The frameshift initiated by ADEx2 is believed to alter the regular coding sequence, acting as a loss-of-function ASIP mutation. In TYRP1 a base substitution was detected in exon 2 (C189T), causing a threonine to methionine change of yet unknown function, and an SNP (A1188G) was found in intron 2.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3' Untranslated Regions
  • 5' Untranslated Regions
  • Adaptor Proteins, Signal Transducing
  • Alleles
  • Animals
  • Base Sequence
  • Carrier Proteins*
  • Cell Adhesion Molecules*
  • Cell Cycle Proteins
  • Cloning, Molecular
  • Color
  • DNA Mutational Analysis
  • Exons
  • Frameshift Mutation
  • Genotype
  • Helminth Proteins / chemistry
  • Helminth Proteins / genetics*
  • Horses
  • Introns
  • Membrane Glycoproteins / chemistry
  • Membrane Glycoproteins / genetics*
  • Methionine / chemistry
  • Models, Genetic
  • Molecular Sequence Data
  • Mutation*
  • Phenotype
  • Polymerase Chain Reaction
  • Receptors, Pituitary Hormone / chemistry
  • Receptors, Pituitary Hormone / genetics*
  • Sequence Analysis, DNA
  • Threonine / chemistry


  • 3' Untranslated Regions
  • 5' Untranslated Regions
  • Adaptor Proteins, Signal Transducing
  • Carrier Proteins
  • Cell Adhesion Molecules
  • Cell Cycle Proteins
  • Helminth Proteins
  • Membrane Glycoproteins
  • Pard3 protein, mouse
  • Receptors, Pituitary Hormone
  • Threonine
  • MSH receptor
  • Methionine