Polymorphism Detections Of ESR,PRLR,RYR1 And RN Loci And Their Associations With Economic Traits In Several Indigenous And Exotic Pig Breeds

Litter size and meat quality are economically important quantitative traits in pig industry, variations of which are under the regulations of polygenes and major genes. Recently, it has been proved that both ESR and PRLR were key factors to regulate the inheritance of reproduction traits in pigs, and both RN and RYR1 were proved to be genes with large genetic effect on meat quality traits as well. Obviously, it is very important to explore the characteristics of genotypic distribution of these loci because it can provide more information to the conservation of indigenous pig breeds and the optimization of heterosis between indigenous and exotic pig breeds. In present study, based upon the PCR-RFLPs technique using restriction enzymes Pvu â…¡, Alu â… , Hha â…  and BsrB â… , polymorphisms in the ESR and PRLP loci were used to genotyping the Chinese Tongcheng and Tibetan pigs, and genotypic variations at RYR1 and RN loci in the Large White and Landrace pigs were detected, respectively. Following these laboratory works, population genetics parameters including allele frequency and genotype frequency were evaluated. The associations between polymorphisms in ESR and PRLP loci and litter size in Tongcheng pigs were analyzed, and the effects of polymorphisms in RYR1 and RN loci on loin area and back fat thickness were also estimated in Tongcheng, Large White, Landrace and their crossbred pigs. The results were as follows:1. Sequences of ESR, PRLR, RYR1 and RN loci were amplified from the genome DNA samples extracted from peripheral blood or hair follicle of Chinese Tongcheng, Large White, Landrace and their crossbred pigs and Tibetan pigs by using the publicly reported primers sequences, the length size of which were 120, 110, 616 and 659 bp, respectively.2. The amplified fragments of ESR, PRLR, RYRland RN loci were digested with restriction enzymes Pvu â…¡, Alu â… , Hha â…  and BsrB â… , respectively. The digested fragments were separated by polyacrylamide gel electrophoresis, and the genotypes on each locus were achieved.3. Evaluation of allele frequency and genotype frequency on ESR and PRLP loci was made, and the results showed that there were three genotypes of AA, AB and BB in all populations except only two genotypes(AB, BB) in Tongcheng pigs.4. Further comparison of allele frequency on ESR locus between indigenous and exotic pig breeds showed a rough tendency that Chinese indigenous pig breed had a larger amount of B allele than that of exotic pig breed. The frequency of B allele in Tongcheng, Neijiang, Taihu, Jinhua and Chenghua pigs was over 60%, while not more than 30% in Duroc, Landrace and Large White pigs. The allelic frequencies of ESR locus in Tibetan pigs were 0.4677 and 0.5323 responding to A allele and B allele, respectively. The frequencies of three genotypes of AA, AB and BB were respectively 0.216, 0.268 and 0.516. The Hardy-Weinberg equilibrium for genotypic frequencies was analyzed with the goodness-of-fit x2 test, and three genotypes were proved to be in equilibrium in which it had been hinted that Tibetan pigs almost didn't accept selection pressure.5. The association of polymorphisms of ESR and PRLP loci with litter size inTongcheng pigs was analyzed with SAS version 8.0 (SAS Institute, Cary, NC). The marginal means showed that ESR locus had significant genotypic effect on litter size. The total number born of BB genotype sows had more 1.84,1.02 and 1.05 piglets than that of AB genotype sows in first parity, second parity and later parities, respectively. The results supported the conclusion that B allele is favorable allele for litter size. For PRLP locus, there were three genotypes, AA, AB and BB, in Tongcheng pigs. The litter size of sows with AA genotype had more 0.7 and 1.06 piglets than that of sows with AB and BB genotypes, respectively. But, sows with BB genotype had 0.32 and 2.06 piglets more than sows with other two genotypes in the second parity. It did not supported that A allele was the favorable allele of PRLP locus in litter size.6. The genotypic interaction effect of ESR and PRLP loci on Utter size was also evaluated in Tongcheng pigs. The marginal means of different gene combinations had not significant difference, and this meant that there was no interaction between ESR and PRLP loci on litter size.7. Generalized linear model, independent variables of which including genotypes of RN locus and population, was resolved with GLM program of SAS version 8.1 for association with loin area and back fat thickness. The results showed that the loin area of pigs with Nn genotype was bigger than that of dominant homozygotes in all pure breeds or three-way crossbreds (P<0.05), in which the loin area of heterozygotes in Landrace X {Large White XTongcheng) three-way crossbreds was 4.8 cm2 bigger than that of NN homozygotes. Additionally, the association between RYR1 locus and average back fat thickness was not detectable in statistics except that there were significant difference between NN and Nn in Tongcheng pigs, which might be made only for the sample size.8. Among the sampled individuals in Tongcheng, Tibetan, Large White and Landrace pigs, the individuals withJRAT/iW and RN~/rn+ genotypes were not detected, and the detected genotype only was recessive homozygote, rn+/rn+.