Genome-wide survey of SNP variation uncovers the genetic structure of cattle breeds.

The imprints of domestication and breed development on the genomes of livestock likely differ from those of companion animals. A deep draft sequence assembly of shotgun reads from a single Hereford female and comparative sequences sampled from six additional breeds were used to develop probes to interrogate 37,470 single-nucleotide polymorphisms (SNPs) in 497 cattle from 19 geographically and biologically diverse breeds. These data show that cattle have undergone a rapid recent decrease in effective population size from a very large ancestral population, possibly due to bottlenecks associated with domestication, selection, and breed formation. Domestication and artificial selection appear to have left detectable signatures of selection within the cattle genome, yet the current levels of diversity within breeds are at least as great as exists within humans.

[Origin and genetic diversity of Mongolian and Chinese sheep using mitochondrial DNA D-loop sequences].

To determine the origin and gene diversity of the Chinese and Mongolian domestic sheep, a partial fragment of mitochondrial DNA D-loop was sequenced for total number of 314 individuals from nine Chinese sheep populations and 11 Mongolian sheep populations. The results show no difference in nucleotide composition between Chinese and Mongolian sheep mtDNA D-loop sequences. However, more variables were identified in Mongolian sheep (26.85% of the sites) than that in Chinese sheep (24.22%). In China, mtDNA haplotype diversity was the highest in Qinghai Tibetan sheep, followed then by Gansu Tibetan sheep, Gansu Alpine Merino, Qinghai Merino, Gannan Tibetan sheep, Small-tailed Han sheep, Tan sheep, Hu sheep and Minxian Black Fur sheep. In Mongolian sheep, mtDNA haplotype diversity was the highest in Bayad and Baidrag populations and the lowest in the Gobi-Altai population. In general, Mongolian sheep have a richer genetic diversity than the Chinese ones with larger number of haplotypes (86.06% (142/165) versus 78.83% (108/137)), higher haplotype diversity (Hd; 0.976 versus 0.936), higher nucleotide diversity (Pi (pi); 0. 036 versus 0.034) and higher average number of nucleotide differences (k; 23.50 versus 22.48). Phylogenetic analysis of the 217 haplotypes identified in both Mongolian and Chinese sheep supported the same origin of their domestication with three distinct maternal lineages defined as major haplotypes A, B and C, of which haplotype A are the commonest in all Chinese sheep populations and in the majority of Mongolian sheep populations (9/11) with an average frequency of 58.73%, followed by haplotype B present in eight of Chinese population and in all Mongolian sheep populations with an average frequency of 24.68%, and haplotype C present in eight Chinese and in 10 Mongolian sheep populations with an average frequency of 16.59%. Further network analysis of the phylogenetic relationship of the 87 haplotypes identified from 91 sequences retrieved from GenBank together with the 217 haplotypes detected in this study reveals clearly four distinct lineages with the European mouflon (O. musimon) mixed into one of the lineages (haplotype B). There is no evidence of contribution of Argali sheep (O. ammon), O. vignei bochariensis and/or O. ammon nigrimontana to the maternal origin of both Mongolian and Chinese domestic sheep.