Genome-Wide Analysis of the World's Sheep Breeds Reveals High Levels of Historic Mixture and Strong Recent Selection
The number of breeds that showed divergent selection is shown as a function of genomic position (A). Selection peaks were defined as regions with smoothed FST in excess of one standard deviation either above (positive selection; blue line) or below the genome-wide average (balancing selection; green line). Four regions were identified with shared positive selection peaks in 30 or more breeds (the chromosomal number is given above each peak). Similarly, five peaks were identified where 20 or more populations shared balancing selection, including the MHC region on OAR 20. One signal was common to each of three separate populations of Texel (B). Pairwise FST was calculated between Texel and all other animals, which revealed a strong selection on sheep Chromosome 2 above the GDF8 gene, which underpins a breed defining phenotype.