Using of Genetic-Population Studies Results for Assessment of Selection Work in Dairy Cattle Populations

Abstract

The article presents the results of complex research that continues previous work aimed at determining the polymorphism of the CSN2, PRL, LEP, and TNF-α loci and analyzing the productivity of dairy cattle with different genotypes for these loci. The goal of the work is to analyze the selection work with populations of dairy cows based on the results of typing individuals for allelic variants of the CSN2, PRL, LEP, and TNF-α loci, which are associated with economically valuable traits but are not directly evaluated by traditional phenotype-based methods. To analyze the data, the observed (Ho) and expected (He) heterozygosity and Wright's fixation index (Fis) were used. Individual animal typing was performed using AS-PCR (CSN2), SSCP (TNF-α), and PCR-RFLP (PRL, LEP) methods. The studies revealed an excess of heterozygous individuals for the CSN2 and TNF-α loci and a significant predominance of homozygous individuals for the LEP locus in the population of Ukrainian Black-and-White dairy cows. For the prolactin (PRL) and leptin (LEP) genes, a deviation from genetic equilibrium was shown due to the increase in the number of homozygous individuals. In the population of Ukrainian Red-and-White dairy cows, a high level of inbreeding (39%) was found for the PRL locus, which was reflected in a deviation from the genetic equilibrium state (χ2 = 13.50). In the case of the beta-casein and leptin loci, the situation is opposite, with a marked excess of heterozygous individuals (-0.24 and -0.18, respectively), but no deviations from the equilibrium state were observed in the population (χ2 values of 2.06 and 2.42, respectively). For both populations, there were no significant changes in the ratio of different alleles and genotypes for several loci investigated, and the impossibility of fixing desired alleles using traditional breeding methods was demonstrated. Based on a comparative analysis of different types of DNA markers and typing methods (AS-PCR, SSCP, and PCR-RFLP), the sensitivity of the Ho, He, and Fis parameters to the number of alleles at the locus was established, which should be taken into account when conducting genetic-population studies. Keywords: polymorphism, population, cows, allele, genotype, homozygosity, variability, fixation.