Comparative analysis of genome-wide copy number variations between Tibetan sheep and White Suffolk sheep.

The DNA copy number variations (CNVs) are widely involved in affecting various kinds of biological functions, such as environmental adaptation. Tibetan sheep and White Suffolk sheep are two representative indigenous and exotic breeds raised in Sichuan, China, and both of them have many contrasting biological characteristics. In this study, we employed high-throughput sequencing approach to investigate genome-wide CNVs between the two sheep breeds. A total of 11,135 CNV regions (CNVRs) consisting of 6,488 deletions and 4,647 duplications were detected, whose length ranged from 1,599 bp to 0.56 Mb with the mean of 4,658 bp. There were 281 CNVRs segregated between Tibetan sheep and White Suffolk sheep, and 18 of them have been fixed within both breeds. Functional analyses of candidate genes within the segregating CNVRs revealed the thyroid hormone signaling pathway and CTNNB1 gene that would be responsible for differential biological characteristics of breeds, such as energy metabolism, seasonal reproduction, and litter size. Furthermore, the segregating CNVRs identified in this study were overlapped with many known quantitative trait loci that are associated with growth, testis weight, and reproductive seasonality. In conclusion, these results help us better understanding differential biological characteristics between Tibetan sheep and White Suffolk sheep.

Genetic diversity and population structure of sheep (Ovis aries) in Sichuan, China.

Sichuan, China, has abundant genetic resources of sheep (Ovis aries). However, their genetic diversity and population structure have been less studied, especially at the genome-wide level. In the present study, we employed the specific-locus amplified fragment sequencing for identifying genome-wide single nucleotide polymorphisms (SNPs) among five breeds of sheep distributed in Sichuan, including three local pure breeds, one composite breed, and one exotic breed of White Suffolk. From 494 million clean paired-end reads, we obtained a total of 327,845 high-quality SNPs that were evenly distributed among all 27 chromosomes, with a transition/transversion ratio of 2.56. Based on this SNP panel, we found that the overall nucleotide diversity was 0.2284 for all five breeds, with the highest and lowest diversity observed in Mage sheep (0.2125) and Butuo Black (0.1963) sheep, respectively. Both Wright's fixation index and Identity-by-State distance revealed that all individuals of Liangshan Semifine-wool, White Suffolk, and Butuo Black sheep were respectively clustered together, and the breeds could be separated from each other, whereas Jialuo and Mage sheep had the closest genetic relationship and could not be distinguished from each other. In conclusion, we provide a reference panel of genome-wide and high-quality SNPs in five sheep breeds in Sichuan, by which their genetic diversity and population structures were investigated.