Analysis of polymorphism in the major genes for reproductive traits in sheep (Ovis spp.)

The reproductive traits significantly affect the cost of production of sheep products. The BMP15, GDF9 and BMPR1B are the major genes for reproduction in sheep, mutations in which increase number of eggs per ovulation and litter size. The segregation of new mutations in an expanding breed diversity has been periodically reported. In this regard, the search for new SNPs in unexplored breeds is relevant to deepen knowledge about the genetic mechanisms underlying sheep prolificacy. In our work, for the first time, a comparative analysis of the complete nucleotide sequences of the GDF9, BMP15 and BMP15B genes in the Romanov sheep was carried out in comparison with other breeds of domestic sheep ( Ovis aries L.) and wild relatives. The most significantly varied SNPs were identified based on comparing the Romanov breed with autochthonous breeds of domestic sheep from Russia and the Persian Highlands, as well as wild Ovis species. Polymorphism in the major genes for reproduction in sheep was studied for argali ( O. ammon L.) and mouflon ( O. orientalis L.) for the first time. SNPs fixed in argali and domestic sheep were identified. The studies were conducted at Ernst Federal Research Center for Animal Husbandry in 2022-2023. We analyzed whole genome sequences of domestic sheep, Romanov ( n = 9), other Russian breeds ( n = 7), Iranian breeds ( n = 6) and wild Ovis species, the Asian mouflon ( O. orientalis , n = 16) and argali ( O. ammon , n = 4). Alignment to the reference genome was performed using bwa-mem2 and SAMtools. The sequences of the GDF9, BMP15, and BMP15B genes were extracted from the whole genomes, in which the most different SNPs were searched based on the calculation of FST values for each SNP for each pair of groups. Gene sequences comparison of the Romanov breed with other breeds showed that the greatest differences were identified in the BMPR1B gene (FST = 0.562-0.749) when compared to the BMP15 (FST = 0.051-0.374) and GDF9 genes (FST = 0.037-0.660). Comparative analysis of gene sequences in the Romanov sheep and argali showed the presence of fixed SNPs (FST = 1), while one such SNP was identified in the GDF9 gene. The highest FST values identified based on comparing Romanov breed sheep with mouflon were 0.702-0.780 ( BMPR1B gene), 0.113-0.645 ( BMP15 gene) and 0.338-0.512 ( GDF9 gene). Thus, target SNPs were identified the effect of which on reproductive traits in the Romanov sheep should be studied in future work.