Study On The Candidate Genes With Fecundity Traits And Their Interaction Effects In Sheep

Llitter size(LS) which determines the number of animals available for utilization, is the key factor that have an greatly affect on profitability of sheep. Generally, most sheep breeds have one or two ovulations but there is wide variation in ovulation rate among different strains influenced by the genetic background and the effects of age, season, nutrition and so on. Recently, many reserches on the genetics of prolificacy in sheep(Ovis aries) lead to highlight the importance of a great quantity major genes which have been shown to affect ovulation rate and litter size through different mechanisms. But further study of the interaction between several other candidate genes have seldom been found. Therefore, in this study we select Hu sheep(171), Small Tail Han sheep(54) and Dorper sheep(47) as the main research object. The main study were as follows:(1)Maked the mixed DNA pools, using Sequenom Mass Array with gene sequencing to analysis the genetic variation of B4GALNT2 and ZAR1 genes in sheep.(2)Used Sequenom Mass Array with the SPSS18.0 to analysis single gene effect on litter size in sheep with 17 main candidate genes(Fec B, GDF9, MTNR1 A, ESR, RBP4, PRL, PRLR, Fec XL, INHA, INHBA, BMP4, FSH-β, IGF-1, IGF-2, PGR, RXRG, Zar1).(3)The interaction effect on litter size with 20 important SNPs in 17 candidate genes was analyzed.(4)The correlation of body measurements traits with important SNPs in 17 candidate genes was analyzed.The main results were as follows:(1)Two polymorphic loci(T5071C, T5138C) of Zar1 gene were first discovered in sheep which all constituting three genotypes. The genotypes of the 2 sites in Hu sheep, Small Tail Han sheep and Dorper sheep were same. The advantage of genotype was CT and genotype frequency was 0.48, 0.51, 0.57 respectively. The dominant allele gene frequency of T was 0.64, 0.55, 0.65 respectively. The results of PIC(0.35, 0.37, 0.35) showed that the groups were moderately polymorphic. The results of He(0.46, 0.50, 0.46) showed that the groups were highly heterozygous. The effective numbers of alleles were 1.85, 2, 1.84 respectively. c2 test indicated three groups were in Hardy-Weinberg equilibrium state. Correlation analysis with sheep economic traits showed that the locus of three genotypes effect on all sheep traits were not significant(p > 0.05).(2)Twenty important SNPs of 17 candidate genes in three different sheep breeds were analyzed.Only three SNPs had been found that being closely relate to the the litter size. The high prolific major gene(Fec B) was closely related with litter size in Small Tail Han sheep. Only two kinds of genotype GG and AG existed in the G605 A locus of MTNR1 A gene in Small Tail Han sheep populations and the mutation sites of MTNR1A(G605A) had a significant impact on litter size. The ewes with AG genotype had 0.48 lambs more than those with genotype GG in Small Tail Han sheep(P = 0.045 < 0.05). In addition, the genotype frequency distribution of GDF9(G477A) mutations in Hu sheep was AA(0.29), GA(0.53) and GG(0.18) responstively; the dominant allele frequency of A was 0.55; the ewes with GA genotype respectively had 0.35 and 0.11 lambs more than those with genotype GA and GG in Hu sheep(P = 0.040 < 0.05).(3)The gene interaction effect of 20 important SNPs in 17 candidate genes which affecting the sheep litter size were analyzed. Seven SNPs were found, including Fec B(A746G), GDF9(G477A), ESR(C363G), PGR(C70T), MTNR1A(G605A), IGF-1(G4988A) and PRLR(G304A). Their mainly interaction effect analysis results were as follows: In Hu sheep(171) :The type of GDF9(G477A) and ESR(C363G) gene pyramiding, the ewes with GG-GG genotype had 1.49 lambs more than those with genotype GA-CC(P = 0.041 < 0.05);The type of Fec B(A746G) and ESR(C363G)gene pyramiding, the ewes with AG-GG genotype had 2.22 lambs more than those with genotype AG-GC(p=0.017<0.05). In Small Tail Han sheep(54):The type of PGR(C70T) and MTNR1A(G605A)gene pyramiding, the ewes with CT-AG genotype had 1.49 lambs more than those with genotype TT-AG(p=0.015<0.05);The type of PGR(C70T) and PRLR(G304A)gene pyramiding, the ewes with CT-GG genotype had 1.09 lambs more than those with genotype CC-AA(p=0.025<0.05). In three varieties combination group(272):The type of GDF9(G477A)and IGF-1(G49888A)gene pyramiding, the ewes with AA-AA genotype had 0.67 lambs more than those with genotype GA-AA(p=0.029<0.05).(4)The results of correlate analysis between multiple SNP sites and body weight of sheep showed that: there had a negative correlation between litter size and body weight of sheep. Which ewe had big litter size, while the light body weight than any other else. The main results were as follows:MTNR1A(G605A) gene effect analysis showed that the ewes with more litter size had significant less weight in Small Tail Han sheep(p=0.019<0.05). The Pearson correlation coefficient was-0.081, showed a significant negative correlation between litter size and body weight of ewes;GDF9(G477A) and ESR(C363G) interaction effect analysis showed that the ewes with more litter size had significant less weight in Hu sheep(p=0.023<0.05). The Pearson correlation coefficient was-0.865, showed a significant negative correlation between litter size and body weight of ewes.In conclusion, genetic variation analysis of B4GALNT2 and Zar1 genes in three different sheep breeds were first conducted in this study. The results showed that these two locus of Zar1 gene have no significant effect with all production traits in sheep. The result of single gene and genes interaction effect on litter size in sheep with 17 main candidate genes showed that there were two locus and five types of gene interaction effect had significant effect on litter size in sheep. The results of correlate analysis between multiple SNP sites and body weight of sheep showed that: Ewes with MTNR1A(G605A) locus and the GDF9(G477A)/ ESR(C363G) gene polymerization type had more litter size but significant less weight. Therefore, the main conclusions were as follows:(1)B4GALNT2 and Zar1 genes were relatively conservative in the evolution in sheep.(2)GDF9(G477A) locus and two types of genes interaction effect [GDF9(G477A) and ESR(C363G)、Fec B(A746G) and ESR(C363G)] that could be choosed as the available molecular markers of litter size in Hu sheep; MTNR1A(G605A) locus and two types of genes interaction effect [PGR(C70T) and MTNR1A(G605A)、PGR(C70T) and PRLR(G304A)] that could be choosed as the available molecular markers of litter size in Small Tail Han sheep.(3)The application of marker-assisted selection should try to avoid the negative effects of relative molecular markers.