In the dissertation, the molecular genetic aspects of the marker-assisted selection implementing into pig breeding of Ukraine were methodologically substantiated using 12 candidate genes of quantitative trait loci: GH, IGF2, RYR1, ESR1, PRLR, CTSL, CTSB, CTSS, CTSK, MC4R, GHRH, and LEPR. A methodology of the application for MAS of molecular genetic information obtained by means of the genetic-population and associative analyses results have been developed. Development and improvement of the DNA-typing techniques by the studied genes has been carried out. The BsuRI polymorphic restriction site was revealed in growth hormone gene. The site is localized in the 1st intron within the range of 474‒477 bp. (GenBank: M17704.1). The methodology to determine the pig genotype according to the revealed growth hormone gene polymorphism has been developed. The genetic-population analysis of pig breeds: Large White pigs (ULW-1 and ULW- 3 intra-breeding types, Large White breed of English selection), Large Black, Landrace, Myrgorod, Ukrainian Steppe White, Ukrainian Steppe Spotted, Poltava Meat has been performed on the genes of quantitative traits loci. The parameters of genetic variability and genetic differentiation of pig breeds were analyzed. On the dendrogram of genetic relationships, which is built on the basis of the genetic distances, breeds form three clusters: breeds of universal type of productivity (Large White breed genotypes) and Meishan, clusters of local pig breeds and meat breeds with a branch of Pietrain. Informativeness of DNA markers of the candidate QTL genes for the purpose of using in associative analysis is estimated. Analysis of the ESR1 and PRLR genes association with the reproductive traits of the Large White and Myrgorod breeds sows has been performed. The association of the ESR1 gene (PvuII-polymorphism) with reproductive traits of sows with the positive effect of the ESR1B allele occurs in the ULW-3. According to data of the 2‒4th farrows, ESR1BB sows have by 1.36 newborn piglets more in the litter than the animals with the ESR1AA genotype (p<0.05). Sows with heterozygous genotype had 0.66 piglets more than sows with ESR1АА genotype. In prolificacy, the sows with the ESR1BB and ESR1AB genotypes, exceeded the animals with the ESR1AA genotype by 1.15 and 0.53 piglets, respectively (p˂0.05). The effect of ESR1/PvuII-polymorphism was characterized by a significant additive component. Statistically significant links between alleles and genotypes of the ESR1 gene with reproductive traits of the ULW-1 sows and the Mirgorod breed have not been detected. The dependence of reproductive traits in the Large White breed sows (ULW-3) on the genotype by the prolactin receptor gene (PRLR / AluI) was established. Sows with PRLRBB genotype exceeded the animals with PRLRAA genotype in the total number of piglets at birth (according to the mean data of 2‒4 farrows) by 1.46 piglets per a litter (p˂0.01), and the sows with PRLRAB genotype ‒ by 1.10 piglets (p˂0.01). In prolificacy, the advantage of PRLRBB and PRLRAB genotype sows over the PRLRAA genotype individuals was at the level of 1.00 (p<0.01) and 0.66 (p<0.05) piglets, respectively. The impact of AluI-polymorphism of the prolactin receptor gene is characterized by significant additive component. Association of the cathepsin B and L, GHRH and LEPR genes with the ULW-1 porcine meat quality was established. With the cathepsin L gene (g.143C>T), the meat of the g.143CC genotype pigs contained the total protein amount greater than that of animals with the g.143CT genotype (21.68 and 20.50 g / 100 g, respectively, p<0.05). Meat of pigs with the heterozygous genotype was characterized by a higher pH (5.59) compared to meat of the pigs with the g.143CC genotype (5.46, p<0.05). Pigs with the BB genotype, by the GHRH gene (AluI-polymorphism) were characterized by a higher content of intramuscular fat than pigs with the GHRHAB genotype (1.9 and 1.4 g/100 g, respectively, p<0.05). The most tender meat was found in heterozygous animals (shear force 40.86 g / cm2), and the most coarse one was in pigs with GHRHBB genotype (49.50 g/cm2) (p<0.001). In animals with c.1987 TT genotype, by the LEPR gene (c.1987C>T SNP), a higher content of intramuscular fat was observed, compared to the pigs of c.1987CT genotype. Pigs with a heterozygous genotype were distinguished by more tender meat compared to pigs with the c.1987СС genotype (shear force 42.89 and 50.71 g/cm2, respectively, p<0.05). DNA markers are suggested for practical use and testing in marker-assisted selection of Large White breed pigs.
