Genetic Analysis Of Polygene Pyramiding On The Reproductive Traits In Goats

Fertility stands for productivity for breeding goat,and which is directly related to the economic benefit of the goat industry.Poor fertility is a major bottleneck restricting the rapid development of goat industry,and research on the nature of genetics is the fundamental way to increase fertility.The polygene pyramiding breeding technology based on molecular marker-assisted selection can be used for directly selecting combinatorial genotypes which influence reproductive performance in molecular level,thus it overcomes the shortcomings of conventional breeding with poor effect and long time.Thus it is the basis and premise to achieve polygene pyramiding breeding technology by screening for molecular markers closely linked with reproductive performance,and researching candidate genes polymorphism with litter size as well as the expression levels on goat tissues.In this study,GnRHR,FSHR,BMP15,BMP6,BMP4,BMPR-IB,BMPR-IA,and GDF9 genes that have important effects on animal fertility were used as candidate genes.It explored the polymorphisms of candidate genes and analyzed the correlation between single nucleotide polymorphisms?SNP?and litter size in 91 Chongqing black goat?CQ?,391 Sichuan black goat?CZ?,290 Leizhou black goat?DS?and 187 Nubian black goat?NS?by the technology of PCR-RFLP,CRS-PCR-RFLP and HRM.At the same time,this study detected the location and expression levels of candidate genes in the tissues of 8 CZ?4 in each group with high fecundity and low fecundity?by qRT-PCR technology.Then,we used bioinformatics and statistical methods to analyse the effect of haplotype block and polygene pyramiding of candidate genes on litter size and determined the best combinatorial genotypes,so that it can be used as molecular marker assisted selection in goats breeding work.The main results of this thesis were as follows:1.The g.75G>A locus of GnRHR gene had a significant effect on the litter size of CZ,CQ and DS?P<0.05?,indicating that this loci could can be used as a molecular marker to influence the fecundity of these three goat breeds.2.The g.-112C>T locus of FSHR gene significantly affected the litter size of CQ and CZ?P<0.05?,while the g.3236C>A site significantly affected the litter size of CZ and DS?P<0.05?,indicating that these two loci can be used as molecular markers that affect the fecundity of goats.3.Among the four goat breeds,the FecX^G mutation of BMP15 gene had no significant effect on litter size?P>0.05?,and there were no mutations of FecX^B,FecX^I,B1,FecX^H and FecX^Gr of the gene,indicating that these six SNPs were more conservative in genetic evolution and cannot be used as a molecular marker that affects the lambing traits of four breeds of goats.4.The g.951T>C locus,first detected in the BMP6 gene,had significant effects on the litter size of CZ,CQ and DS?P<0.05?,indicating that this loci could be used as a molecule marker that affects the fertility of these three goat breeds.5.There were no polymorphic loci in BMP4,BMPR-IA,BMPR-IB and GDF9 genes that affect the fecundity of the goats,indicating that the gene sequences within the detected gene fragments were relatively conserved,and the polymorphic loci that affect the high fecundity of goats may be located in other functional areas of these genes.6.The high expression of GnRHR,FSHR,BMP15,BMP6 and GDF9 genes in the ovary or pituitary of CZ may be an important reason for producing multiple eggs and lambs in goats.7.Genetic analysis of polygene pyramiding showed that AATTCC was the best combination genotype of CQ;AACCAACC was the best combination genotype of CZ;AAAACC and AACCCC were the best combination genotypes of DS;and these combination genotypes had significant effects on the litter size of goats?P<0.05?.To sum up,the AA type of the g.75G>A site,the TT type of the g.-112C>T site,AA type of the g.3236C>A site and the CC type of the g.951T>C site are all the excellent alleles.Selecting the excellent alleles of these molecular markers in the breeding work can accelerate the genetic progress of litter trait and reduce the breeding time of the goat,and it can improve effectively the economic benefits of breeding goat.In addition,the analysis of the polygene pyramiding of these SNPs showed that:If AATTCC genotype individuals were selected,the average number of lambs per goat could be increased by 0.67 compared to GACTCC genotype in CZ;If AACCAACC genotype individuals were selected,the average number of lambs per goat could be increased by 0.96 compared to GACCCCCC genotype in CZ;If AAAACC genotype and AACCCC genotype individuals were selected,the average number of lambs per goat could be increased respectively by 0.67 and 0.46compared to GACCCCCC genotype in DS.It can be seen that screening goat with excellent reproductive performance has great potential in the goat industry.