Genetic Diversity And Molecular Markers Screening Of Important Economic Traits In Tianhua Mutton Merino

In the early stage,the team spent 14 years in Tianzhu Tibetan Autonomous County,an important production area of fine wool sheep in China,creating new germplasm containing 62.5%lineage of South African mutton merino sheep and 37.5%lineage of Gansu alpine fine wool sheep.Then the team completed crossbreed and cultivated a new mutton merino breed-Tianhua mutton merino sheep（TZ）.In this paper,the genetic diversity of TZ cross-fixed offspring was studied from three aspects of mtDNA,Y chromosome gene and autosome gene,and the molecular markers related to economic traits were screened to provide technical guidance for the breeding of new varieties.The main research results of this paper were as follows:（1）The mtDNAD-loop of 84 TZ was sequenced and then combined analyzed with the sequences of 15 Gansu alpine fine wool Sheep（GX）,11 South Africa mutton merino（SM）,14 Alpine merino（GSM）and 16 Qinghai fine wool sheep（QHM）.A total of 79 haplotypes were identified.TZ has 56 haplotypes and 43 are unique.The nucleotide diversity and haplotype diversity of TZ were 0.039 and 0.980,respectively.Phylogenetic tree analysis showed that TZ gathers with QHM,GSM and GX;Most individuals in the SM group gather as a single branch.（2）The Y-SNPs of 212 rams TZ（n=195）,SM（n=11）and GX（n=6）were researched using 45 pairs of Y chromosome primers.Four Y-SNPs were identified,including DDX3Y5:g.688 A>G,SRY16:g.3116 C>T,ZFY16:g.904 C>T,EIF2S3Y6:g.101435 A>G.Association analysis showed that three Y-SNPs significantly affected the scrotal circumference of yearling TZ;11 Y haplotypes in TZ population were constructed,among which the haplotype GTCG was the main haplotype,and the haplotype also had a significant effect on the scrotal circumference of TZ.（3）The genomes of 120 sheep（TZ（n=98）,SM（n=11）and GX（n=11））were re-sequenced.Principal component analysis（PCA）,population structure and phylogenetic tree analysis showed that TZ could be separated from GX and SM and basically become an independent branch.37 SNPs related to economic traits were screened by genome-wide association studies（GWAS）,of which 8 SNPs were significantly related to body weight and body size,5 SNPs related to backfat thickness,eye muscle area and eye muscle thickness,and 24 SNPs related to wool length and greasy wool production.Gene annotation found that significant SNPs were mainly located in MAN2A1,TIGD4,TMEM154,GTF3C1,COL4A1,FAM3D,APPL2,KCNMA1,RAC2,IGFBP3,POMC,RBFOX3 etc.Functional annotation showed that these genes were mainly related to protein digestion and absorption,lipid transport,regulation of transmembrane transport,the positive regulation of cell proliferation and other pathways.In conclusion,this study found that the new breed population of Tianhua mutton merino sheep has rich maternal genetic diversity;Four Y-SNPs were identified,of which three were significantly related to the scrotal circumference of rams.Eleven Y haplotypes were constructed,and the Y haplotype also had a significant effect on the scrotal circumference of rams;Based on GWAS,37 SNPs related to body weight,body size,wool production and meat production were screened,which provided reliable molecular markers for the cultivation of new varieties.