Identification of the Basic Coat Color Genes in the Dromedary (Camelus dromedarius)

Mammalian color phenotypes are determined by a few major and a larger number of modifier genes. Among the major coat color genes, the melanocortin 1 receptor (MC1R), the agouti signaling protein (ASIP), and tyrosinase related protein 1 (TYRP1) are the main regulators of the production of black/brown pigment (eumelanin) and the red/yellow pigment (pheomelanin). Mutations in these genes have been associated with different colors in several species, though not yet in dromedaries. Here we investigated association of sequence variants of MC1R, ASIP, and TYRP1 with basic coat colors - white, black and red - in the dromedary. Sequencing coding regions of MC1R, ASIP, and TYRP1 in dromedaries from Saudi Arabia identified a missense mutation in MC1R domain that was associated with white color (P <0.0001). Homozygosity for a single nucleotide frameshift deletion in ASIP causing a premature STOP codon was associated with black color. Though, some black dromedaries were heterozygous for the deletion suggesting that additional mutation(s) in the ASIP gene might contribute to the black phenotype. None of the three colors, however, was associated with variants in TYRP1. The red color most likely is the wild type, though additional modifier genes might regulate the intensity of this color ranging from beige to deep red. Comparison of dromedary and alpaca MC1R and ASIP showed that color phenotypes in the two species are regulated by different mutations in ASIP and MC1R. The findings lay a foundation for developing molecular tests for coat color in dromedaries.