Population Structure and Genetic Diversity of Tibetan Sheep Revealed by Whole-Genome Resequencing: Implications for Conservation and Breeding

Background: Tibetan sheep (Ovis aries) have evolved remarkable adaptations to the extreme high-altitude environment of the Qinghai–Tibet Plateau. While previous studies have identified some genetic features underlying these adaptations, a comprehensive understanding of their population genetics and selection signatures remains incomplete. We hypothesized that Tibetan sheep harbor unique genetic diversity and population structure distinct from low-altitude sheep (Hu sheep and Small Tail Han sheep), and that whole-genome resequencing could identify key positively selected genes driving their high-altitude adaptation and economic trait variation. Thus, this study aimed to characterize the population structure and genetic diversity of Tibetan sheep via whole-genome resequencing and identify genomic regions and candidate genes under positive selection related to high-altitude adaptation and important economic traits (growth, meat quality, wool, reproduction). Results: Using whole-genome resequencing of 90 Tibetan sheep (ZY) compared to 90 Hu sheep (HY) and 90 Small Tail Han sheep (XWHY), we identified significantly higher genetic diversity in Tibetan sheep (Pn = 0.6399, PIC = 0.1731). Population structure analyses revealed distinct clustering of Tibetan sheep, with principal components explaining 20.69% (PCA1), 12.26% (PCA2), and 14.18% (PCA3) of genetic variation. Selective sweep analysis identified 713 genomic regions (containing 207 genes) under positive selection, including key hypoxia adaptation genes (HDAC5, BMP2/BMPR1B, DUOX2) and economic trait genes (FGF9 for growth; SLC27A2 for meat quality; KRTAP for wool; IZUMO1R for reproduction). Functional enrichment highlighted pathways in oxygen transport (EPO regulation), energy metabolism (fatty acid β-oxidation), and vascular remodeling (TGF-β signaling). Conclusions: Our study provides the most comprehensive genomic characterization of Tibetan sheep to date, revealing both their unique genetic diversity and molecular mechanisms of high-altitude adaptation. The identified candidate genes offer valuable targets for marker-assisted breeding to improve productivity while maintaining adaptive traits, supporting sustainable development of plateau animal husbandry.