Novel graphical analyses of runs of homozygosity among species and livestock breeds

Runs of homozygosity (ROH), uninterrupted stretches of homozygous genotypes resulting from parents transmitting identical haplotypes to their offspring, have emerged as informative genome-wide estimates of autozygosity (inbreeding).We used genomic profiles based on 698K single nucleotide polymorphisms (SNPs) fromnine breeds of domestic cattle (Bos taurus) and the European bison (Bison bonasus) to investigate how ROH distributions can be compared within and among species. We focused on two length classes: 0.5-15Mb to investigate ancient events and >15Mb to address recent events (approximately three generations). For each length class, we chose a few chromosomes with a high number of ROH, calculated the percentage of times a SNP appeared in a ROH, and plotted the results. We selected areas with distinct patterns including regions where (1) all groups revealed an increase or decrease of ROH, (2) bison differed from cattle, (3) one cattle breed or groups of breeds differed (e.g., dairy versus meat cattle). Examination of these regions in the cattle genome showed genes potentially important for natural and humaninduced selection, concerning, for example, meat and milk quality, metabolism, growth, and immune function. The comparative methodology presented here permits visual identification of regions of interest for selection, breeding programs, and conservation.