Whole-Genome SNP Study of Romanov Sheep

The Romanov breed stands out from the global variety of sheep breeds. Romanovs originated from local sheep at the end of XVII century in the Volga Valley. Since 1970's the breed has become popular in France, Canada and the USA. Some unique traits are of permanent interest to this Russian breed. Primarily, Romanovs have outstanding reproduction qualities: early sexual maturity, out-of-season breeding ability and extraordinary prolificacy. Using of the Romanov ewes in crossbreeding programmes is a profitable practical method to increase the number of highly viable hybrids. In addition, the Romanov breed has unique wool properties, which is very suitable for manufacturing felt products, rugs, mats. However, detailed genetic information on the breed is lacking. Thus, we performed the whole-genome SNPs analysis of the original Romanov sheep to study its genetic diversity and genetic relationships with other Russian breeds. We genotyped 42 samples of Romanovs using OvineSNP50K BeadChip and pooled together the data with the set from 24 Russian breeds. Quality filtering was performed in PLINK v1.07. Calculations were done in PLINK v1.07, GENETIX v.4.05, HP-Rare 1.1. We found lower level of genetic diversity in Romanovs (Ho=0.350; Ar=1.862) in comparison with other coarse wool breeds (Ho=0.377; Ar=1.899). At the same time, Romanovs compared to 24 breeds were characterized by the most insignificant deviation from Hardy-Weinberg equilibrium (Fis =˗0.005). In other breeds, Fis values varied from ˗0.028 to ˗0.082. Pairwise Fst values ranged from 0.084 to 0.124 between Romanovs and Kuibyshev and Kuchugur, respectively. The MDS analysis revealed the genetic uniqueness of Romanov sheep. The PC1 divided all breeds into two groups according the wool type (fine wool + semi fine wool and coarse wool) with 4.7% of total genetic variance. By PC1 the Romanov formed an incorporate bunch and logically clustered with coarse wool breeds. However, the Romanov was clearly separated from others by PC2, which explained 3.8% of additional genetic variability. Most likely, a high level of consolidation and genetic differentiation of the Romanov breed from other Russian sheep are explained by its «pure gene» origin and was not improved by any breed. Our study is the first attempt to reveal outstanding genetic nature of original Romanov sheep on whole-genome level. We will extend our study by genotyping more samples with medium-density DNA-chip and using NGS technology. The research was performed under financial support of Russian Scientific Foundation (№ 14-36-00039).