Studies On Candidate Genes PTGS2 And PRL For High Prolificacy Of Small Tail Han Sheep

The methods of PCR-SSCP and PCR-RFLP were established in this study. Based on the genetic polymorphism of PTGS2 gene and PRL gene, we try to link these candidate genes with the high productivity of Small Tail Han sheep, to further provide scientific evidence for the basic genetic research on Small Tail Han sheep high productivity.Applying the powerful PCR-SSCP and PCR-RFLP technique to analyze the polymorphism of prostaglandin-endoperoxide synthase 2 gene and prolactin gene, we divided our samples into two groups, one group is the blood sample of Small Tail Han sheep; another group is the blood sample of four different sheep breeds without littering records (Hu sheep, Texel sheep, Suffolk, Dorset). The results were as follows: fragments amplified by two primers of PTGS2 gene showed that the fragment amplified by primer 1 namely promoter region didn't exhibit polymorphism by SSCP analysis, that the fragment amplified primer 2 namely region of spanning from exon 3 to exon 5 exhibited base difference by RFLP analysis. Thereinto 936 locus was polymorphic locus, when this locus exhibited base mutation, 420bp and 516bp were digested. All five sheep breeds had two genotypes (AA and AB) and two alleles (A and B).A gene frequency was significantly higher than B gene frequency. The difference of the genetic characteristic (heterozygosity, polymorphic information content (PIC) and effective number of alleles) was not evident in five sheep breeds. The effective number of alleles, heterozygosity and PIC of Texel sheep were least at this locus. They were 1.0951,0.0869,0.0831 separately. The effective number of alleles, heterozygosity and PIC of Suffolk sheep were most. They were 1.4204,0.2960,0.2522 separately. As for polymorphic information content, except Suffolk sheep achieving moderate polymorphism, other four sheep breeds were all intermediate polymorphism.X2 fitness test showed that fragment amplified by primer 2 is in a state of Hardy-Weinberg Equilibrium.Among Small Tail Han sheep with littering records, least squares analysis showed that fragments amplified by primer 2 had no significant effects on the first littering records and the second littering records .Fragments amplified by two primers of PRL gene showed that the fragment amplified by primer 2 namely exon 5 region didn't exhibit polymorphism by SSCP analysis, that the fragment amplified primer 1 namely 5＇flank region exhibited base difference by SSCP analysis. Olny Small Tail Han sheep with littering records had two genotypes (AA and AB) and two alleles (A and B). A gene frequency was significantly higher than B gene frequency. The effective number of alleles, heterozygosity and PIC of were 1.0960,0.0878,0.0839 separately, The PIC belonged to intermediate polymorphism. Only one allele was found in other four sheep breeds without littering records. X2 fitness test showed that fragment amplified by primer 1 was in a state of Hardy-Weinberg Equilibrium. We cloned and sequenced fragment amplified by primer 1,which included one mutation locus.Our sequences show that there was one mutation (C→A) in 63bp of 5＇flank of prolactin gene. Maybe the locus mutation had influence upon transcription and regulation, but need studies to conform it.Among Small Tail Han sheep with littering records, least squares analysis showed that fragments amplified by primer 1 had significant effects on the first littering records (P<0.05), AB genotype was much more 0.5 than AA genotype, and also had significant effects on the second littering records (P<0.05), AB genotype was much more 0.57 than AA genotype.According to all of our results, we conclude that the polymorphism of fragment amplified by primer 2 of prostaglandin-endoperoxide synthase 2 gene and fragment amplified primer 1 of prolactin gene probably associated with Small Tail Han sheep productive trait, but need further studies.