Genetic diversity of Bos grunniens bred in the Tien Shan of the Kyrgyz Republic

The mountain range pastures, which occupy 90 % of the territory of the Kyrgyz Republic, are highly favorable for the development of yak breeding. Yaks ( Bos grunniens ) are exclusively pasture-based animals that are well-adapted to living in harsh high-mountain climatic conditions. Only a few countries in the world engage in yak breeding, and the Kyrgyz Republic has been breeding yaks since ancient times. The migration of yaks in the Tien Shan Mountains proceeded from south to north. During the evolutionary process in the Tien Shan and Pamir-Alai Mountains, a specific type of high-mountain yak was formed, exhibiting eight distinct coat colors, ranging from black and brown to variegated and light brown. It became necessary to clarify the genetic structure of the existing yak population in order to compile a preliminary genetic reference group of unique animals. In this study, the molecular genetic status of yaks bred in the high-mountain region of the Tien Shan of the Kyrgyz Republic was determined for the first time using microsatellite DNA markers. Specific characteristics that distinguish the Kyrgyz yak population from other geographic groups of these animals were identified, significantly contributing to the understanding of its genetic features. The obtained data also enable an assessment of genetic diversity and inbreeding risks in Tien Shan yak populations, which is crucial for developing conservation strategies and rational utilization of these animals. The aim of our research is to assess the genetic diversity of the domestic yak population bred in the highland region of the Tien Shan in the Kyrgyz Republic using DNA microsatellite markers. The study was conducted in 2021-2023 at the Research Institute of Molecular Biology and Medicine (Bishkek, Kyrgyz Republic) and the Institute of Genetics and Cytology (Minsk, Republic of Belarus). The research material was blood samples collected from an adult herd of 55 domestic yaks bred in the highland region of Kalmak-Ashuu (Kochkor district, Naryn region, Kyrgyz Republic). The samples were genotyped for 15 microsatellite loci: ETH3, INRA023, TGLA227, TGLA126, TGLA122, SPS115, ETH225, TGLA53, BM2113, BM1824, ETH10, BM1818, CSSM66, ILSTS006, and CSRM60. PCR was performed using Multiplex PCR Master (Jena Bioscience, Germany) in a multilocus format according to the manufacturer’s recommendations. The amplification products were then combined and subjected to fragment analysis. The PCR results were analyzed by capillary electrophoresis using an automatic genetic analyzer with laser-induced fluorescence detection, Applied Biosystems 3500 (Thermo Fisher, USA). Samples validated using the COrDIS Cattle kit (GORDIZ LLC, Russian Federation) served as controls. The analysis of population genetic parameters and the degree of differentiation based on the genetic distance matrix was performed using GenAlEx 6.503 software, with subsequent visualization of dendrograms using the Neighbor-joining algorithm in the Past v.4.03 program. The genetic structure of the studied yak sample was assessed by clustering in the STRUCTURE 2.3.4 program. The optimal number of clusters (ΔK) was determined using the POPHELPER v1.0.10 web application. In the 15 autosomal STR loci of the studied sample, 89 alleles were identified, 32 of which were rare (with an occurrence frequency of less than 5.0 %). Based on the assessment of genetic and population parameters (Na = 5.933±0.316, Ne = 3.015±0.235, Ho = 0.617±0.049, PIC = 0.581±0.130), a conclusion was made about the high values of genetic diversity in the studied yak sample. An electronic database of individual genotypes was created to form a reference group of yaks characterizing their genetic diversity in the region. The breeding schemes for domestic yaks in the high-mountain region of the Tien Shan are balanced and contribute to the preservation of genetic diversity. A comparative analysis of the results of this molecular genetic study with those of other similar works allows us to conclude that domestic yaks ( Bos grunniens ) bred in the Tien Shan of the Kyrgyz Republic exhibit significant genetic diversity.