Estimation of runs of homozygosity reveals moderate autozygosity in Northern European sheep breeds

Runs of homozygosity (ROH) stretches are continuous homozygous fragments of the genome, which are more suitable for calculating the genomic inbreeding, identifying footprints involved in economic traits and understanding the population history in livestock species. In this study, using a dataset of Ovine SNP50 BeadChip genotypes, the distribution of ROH in nine sheep populations (Soay n= 110, Australian Poll Dorset n=108, Australian Suffolk n=109, Finn sheep n= 99, Scottish Texel n= 80, Scottish Blackface n= 56, Galway n= 49, Border Leicester n= 48, German Texel n=46) from Europe were investigated. ROHs were detected by using PLINK v1.09 with the minimal number of SNPs in ROH set at 40; the maximal gap between the adjacent SNPs was set to 1Mb; the minimum SNP density per ROH was set to 1/100 kb and no heterozygote less than 16 Mb was allowed. The detected ROHs were specified to four categories, based on their length: 1–4 Mb, 4–8 Mb, 8–16 Mb and above 16 Mb. A total of 22,204 ROHs were identified, in which ~ 92 – 98 % were less than 16 Mb in length, covering 4.6% to 12.9% of the entire genome. The inbreeding coefficient based on ROH (FROH) varied among populations (ranging from 0.05 to 0.14). The highest inbreeding rate was found in Border Leicester and Soay breeds. In addition, we detected 90 possible ROH Islands that overlapped with candidate genes associated with different economic traits such as the body weight, meat production, fat deposition, horn-less, and coat color in sheep. Our results suggested that although genetic selection for meat and wool traits in these breeds have been extensively carried out during the last decades, the autozygotic proportion of the genome is still considerably low, and it could lead to an acceptable response to selection in breeding schemes.