Ovine Domestication and Diversity

Abstract

Sheep are a highly versatile and adaptable domestic species. Dissection of the genetics responsible for the ovine domestic phenotype relies on an understanding of the genetic variability that resides within and between breeds and also knowledge regarding both the maternal and paternal origins of sheep. Mitochondrial DNA was investigated in the search for novel 'Ovis aries' matrilines and the complete mitogenome sequenced from a subset of domestic and wild sheep to resolve the phylogenetic relationships between these groups. A fifth domestic lineage was identified in sheep from the Near East, a proposed centre of domestication. Mitogenome analysis revealed no wild sheep introgression in the five 'O. aries' groups. To contrast this maternal picture, variation in the male-specific region of the ovine Y chromosome was investigated. Seven novel single nucleotide polymorphisms and a previously uncharacterised microsatellite from the ovine sex determining gene region were used to generate 17 paternal haplotypes. Analysis of these markers across wild and domestic sheep again failed to identify signatures of wild Ovis introgression in modern sheep. The emerging picture of male mediated domestication suggested that there are at least two patrilines present within 'O. aries'. One of these has a possible European origin and the other, a less restricted distribution. Genetic diversity and linkage disequilibrium (LD) was characterised using autosomal microsatellites. Five domestic populations were investigated, with the result that in genetically diverse breeds, LD extended for only short distances, whilst more homogeneous populations displayed extensive patterns of LD. This clearly illustrated the impact of population history on the extent LD and will inform subsequence gene mapping studies in sheep. The three classes of genetic variation investigated (autosomal, paternal and maternal), each reveal aspects of the genetic architecture present within domestic sheep and only by assaying each of these, will the true picture of ovine domestic and diversity be revealed.