Assessment of the genetic diversity of cattle by marker genes of dairy productivity

Absrtact. The paper presents an assessment of the genetic diversity of cattle by the genes of dairy productivity: kappa-casein (CSN3), beta-casein (CSN2), beta-casein A1A2 (CSN2 A1A2) and genes involved in the regulation of milk production: fatty acid synthase (FASN), thyroglobulin (TG5), diacylglycerol O-acyltransferase 1 (DGAT 1), anti-pituitary-specific transcription factor-1 (PIT-1 /Hinf I). Blood samples of 90 cows (Yaroslavl purebred - 39 heads, Holstein purebred - 21 heads and crossbreeds of Yaroslavl and Holstein breeds with a blood content of 75...88% - 30 heads) of breeding farms of the Yaroslavl region served as the material for the study. The studied groups of animals showed gene polymorphism and the presence of two alleles with the exception of the DGAT1 gene, which is monomorphic. In the group of purebred Yaroslavl cows, only one A allele was found according to the PIT-1/Hinf I gene. The lack of heterozygotes in all animal groups was observed in the kappa and beta-casein loci (Fis = 0.0...0.42 and 0.21...0.42, respectively). This is due to the long-term selection of milk components. Among the studied animals, the greatest genetic variance is accounted for by individual diversity - 82%. Only 5% of the total dispersion is due to the presence of different breeds. Based on the cluster analysis, three clusters were identified, while the genetic distances were statistically significant in a group of purebred Yaroslavl cows with individuals of the Holstein breed and crossbreeds (Fst = 0.099 and 0.049, respectively). All the studied genes form two components that explain the genetic differentiation of the studied groups. The first component explains 49.5% of the total variance of the genotypes of the studied animals, and includes identification by genes responsible for regulating milk production. The proportion of the explained variance of the second component, which is negatively correlated with the genes encoding milk proteins: kappa- and beta-casein, is lower and amounts to 15.3%.