The Polycerate Trait in Jacob and Navajo-Churro Sheep may be Located on Ovine Chromosome 2

A genome-wide association study (GWAS) has been used to identify the genetic region underlying an unusual trait in Navajo-Churro (NC) and Jacob (J) sheep.  Both breeds have polycerate (multi-horned) animals where the number of horns ranges from one to six. In this study, genomic DNA was collected from 38 Navajo-Churros and 127 Jacob sheep and genotyped with the Illumina Ovine Infinium HD SNP BeadChip. Horn type was scored in all 165 animals and ranged from zero horns (polled) to five horns.  Scurs (incomplete bone growth) were also present in 24 animals.  The polled trait has been previously mapped to the RXFP2 gene located on ovine chromosome 10 (OAR10) at position 29.54 Mb.  This gene has been reported to account for the presence of horns in Soay sheep.  In our analysis, a strong association signal was identified on OAR10 in the region of the RXFP2 gene in a comparison of polled (n = 10) and horned (n = 131) animals.  In a separate analysis of animals with two (n = 58) or four (n = 68) horns, a highly significant association was detected for SNP on OAR2 at Mb position 132.  Thus, the genetic determinant controlling the appearance of four or more horns appears to be separate from RXFP2 which has an established role in poll and horn diameter.  These results contribute to the characterization of genetic variation that exists within the Ovis aries species.