Interaction of MC1R and PMEL alleles on solid coat colors in Highland cattle.

Six solid colors occur in Highland cattle: black, dun, silver dun and red, yellow, and white. These six coat colors are explained by a non-epistatic interaction of the genotypes at the MC1R and PMEL genes. A three base pair deletion in the PMEL gene leading to the deletion of a leucine from the signal peptide is observed in dilute-colored Highland cattle (c.50_52delTTC, p.Leu18del). The mutant PMEL allele acts in a semi-dominant manner. Dun Galloway cattle also have one copy of the deletion allele, and silver dun Galloway cattle have two copies. The presence of two adjacent leucine residues at the site of this deletion is highly conserved in human, horse, mouse and chicken as well as in cattle with undiluted coat colors. Highland and Galloway cattle thus exhibit a similar dose-dependent dilution effect based on the number of PMEL :c.50_51delTTC alleles, as Charolais cattle with PMEL :c.64G>A alleles. The PMEL :c.64G>A allele was not found in Highland or Galloway cattle.