**5. Conclusion**

High mtDNA genetic diversity in the sheep from the Qinghai-Tibetan Plateau areas is a rich resource for China. The evidences indicate the high diversity of four maternal lineages by doing the large-scale mtDNA D-loop sequences analysis of 15 Tibetan sheep populations. Although the maternal lineage D was only found in a single LZ, phylogenetic analysis showed that four maternal lineages (A, B, C and D), previously defined, could be identified in the 636 tested individuals of the 15 Tibetan sheep populations. The estimation of demographic parameters from the mismatch analyses shows that maternal lineages A, B and C had at least one demographic expansion in the Tibetan sheep of the Qinghai-Tibetan Plateau areas.
