Genomic scan of selective sweeps in thin and fat tail sheep breeds for identifying of candidate regions associated with fat deposition

Two independent experiments using either Iranian or Ovine HapMap genotyping data contrasted thin and fat tail breeds. Population differentiation using FST in Iranian thin and fat tail breeds revealed seven genomic regions. Almost all of these regions overlapped with QTLs that had previously been identified as affecting fat and carcass yield traits in beef and dairy cattle. Study of selection sweep signatures using FST in thin and fat tail breeds sampled from the Ovine HapMap project confirmed three of these regions located on Chromosomes 5, 7 and X. We found increased homozygosity in these regions in favour of fat tail breeds on chromosome 5 and X and in favour of thin tail breeds on chromosome 7.In this study, we were able to identify three novel regions associated with fat deposition in thin and fat tail sheep breeds. Two of these were associated with an increase of homozygosity in the fat tail breeds which would be consistent with selection for mutations affecting fat tail size several thousand years after domestication.The domestication of livestock represents a crucial step in human history. The rise of civilizations could not happen without domestication of plants and animals. Sheep (Ovis aries) is the first grazing animal known to have been domesticated [1]. Multiple mitochondrial lineages suggest that domestication occurred several times, as in other livestock species such as cattle, goat and pig [2]. Recognition of the origin of domestication is difficult by the fact that the first domestic animals were no different from their wild counterparts [3]. In spite of this, the archaeozoological evidence suggests that the domestication of sheep occurred during the Neolithic revolution approximately 9000 years ago [4] in a region in northern Iraq and nearby regions in Iran [5]. Since domestication, sheep have established in a wide geographical range due to their adaptability to poor nutrition diets, tolerance to extreme climatic conditions and their manageable size