Abstract:

The Maiwa yak， a breed of domestic yak， is an excellent yak strain for meat and milk production on the Qinghai-Tibetan Plateau. This study explored the genetic diversity and genetic structure of the Maiwa yak population in Longri Breeding Farm in Sichuan Province. A key aim was to identify genes important to defining germplasm categories and thereby evaluate the conservation status of three preserved populations. We used genotyping-by-sequencing （GBS） technology to categorize three preserved populations： The ‘pink mouth’ population （FZ） （n=140）， the ‘full black’ population （QH） （n=211） and the ‘gray coat’ population （FL） （n=55）. Analysis of the resulting sequences identified 126122 single nucleotide polymorphism （SNP） markers which were used to calculate genetic statistics such as observed heterozygosity （Ho）， inbreeding coefficients （Fis）， genetic differentiation index （Fst）， and genetic distance （DR）. The average observed heterozygosity values and average expected heterozygosity values （He） of the whole Maiwa yak population were 0.3038 and 0.3036. The genetic diversity of Maiwa yak was high. The Ho values of QH， FZ and FL were 0.3029， 0.3042， 0.3044， respectively， while the Fis values were 0.0144， 0.0152， 0.0209， respectively. The intensity of artificial selection of FL and FZ was greater than QH， and the lower inbreeding level showed that the conservation status of the three preserved populations was better in Longri Breeding Farm. Structure analysis showed that the pedigree of some individuals in QH and FL is pure， while the pedigree of other individuals is extremely mixed. The Fst and DR of FZ and QH populations were 0.03513 and 0.0358， respectively. The genetic distance between FZ and QH was the greatest and there was obvious genetic differentiation between them； This result was consistent with a constructed phylogenetic tree. In addition， we also performed a selective signal analysis of the three preserved populations using Fst and π methods. The 104 selected genes were involved in a wide range of metabolic processes， including reproductive function， the immune system， embryonic development， lipid metabolism and others， as well as signal transduction， reproductive hormone， endocrine/exocrine， and other signal transduction pathways. Some of them， such as PPP3CC， KCNMA1， ROCK2， GNAQ， MEF2C， and KIT geneswere related to reproduction， meat quality， coat color traits and stress response of Maiwa yaks. In conclusion， the existing conservation strategy of Maiwa yak is tenable. The study provide genetic reference data for future conservation breeding and genetic improvement of Maiwa yak.

Key words: Maiwa yak, GBS, genetic diversity, genetic structure, selective signal