Genome-wide Association Analysis Of Carcass Fat Traits Of F₂ Crossbred Between Texel And Kazakh Sheep

Genome-wide Association Analysis（GWAS）screens out SNP sites that are significantly related to traits,so as to quickly and accurately locate functional genes,which plays an important role in the identification of candidate genes for animal traits.The purpose of this study is to use the 8-month-old cross F₂ generation of low-fat lean-tailed sheep Texel and local fat-tailed Kazakh sheep（Kazakh Sheep）as the research object,using sheep Illumina 600KSNP chip using Rmvp software Using the method of mixed linear model to screen the SNPs that are significantly related to fat traits,refer to the sheep genome（Ovis＿aries＿v4.0）to annotate the significantly related SNPs found in GWAS,and combine gene functions to determine candidate genes related to fat traits.The research content is as follows:1.Using principal component analysis in SPSS software,the principal component analysis of 41growth traits and carcass-related phenotypic traits of 520 individuals of Texel×Kazakh sheep in the2014-2019 hybrid second-generation herd was carried out,and it was found that Fat traits have a higher contribution rate;using the K-Means cluster analysis in the R language,the pre-slaughter weight,weaning weight,tail fat weight,back fat weight,kidney fat weight,mesenteric fat weight and GR value of this population are 8 Personality traits are divided into four categories according to the similarity between the phenotypic traits.The tail fat weight appears to be group-differentiated.The results suggest that individuals with type B（moderate tail fat）have the best phenotypic results.2.Using the mixed linear model in the Rmvp software to analyze the tail fat weight,back fat thickness,kidney fat weight,mesenteric fat weight and GR value of 520 hybrid second-generation populations,five carcass fat traits,GWAS analysis,at the genomic level It was found that there were 6SNPs significantly related to tail fat weight,19 SNPs significantly related to back fat thickness,9 SNPs significantly related to kidney fat weight,2 SNPs significantly related to mesenteric fat weight,and 9SNPs related to GR Values are significantly related to SNPs.Gene annotation of significantly related SNPs by referring to the sheep genome（Ovis＿aries＿v4.0）.Using the online gene enrichment software DAVID to perform functional enrichment analysis on the obtained candidate genes,a total of 55 genes were identified;combined with gene function analysis,the SCD was initially determined,CTBP1 and CREB1 genes are candidate genes that affect fat weight in the tail,POU1F1,LBP,FFAR4 and SKOR1genes are candidate genes that affect back fat thickness,FFAR3 genes may be candidate genes for kidney fat weight,LIPJ,LIPK,LIPN and LIPM Genes may be candidate genes that affect kidney fat weight,PPARαand ESR1 genes are candidate genes that affect GR value3.SNP sites affecting fat traits were screened from FFAR4,SKOR1,LIPJ candidate genes related to carcass fat traits,and mutant bases were detected in 214 second-generation hybrids with resequencing data in 2018 and 2019.,Through SPSS software for one-way analysis of variance,Phyre2 software for protein structure analysis,protein physical and chemical properties analysis and expression analysis.Results In the analysis of the correlation between the genotype and phenotype of FFAR4,SKOR1 and LIPJ genes,7 loci were significantly related to fat traits;and changes in the amino terminus of FFAR4and LIPJ genes in the CDS region may cause local structural changes in the protein;Expression analysis also found that the two sites of FFAR4 and LIPJ genes located in the 3’UTR region were significantly related to fat traits.In summary,it is believed that FFAR4,SKOR1 and LIPJ genes are candidate genes that affect fat traits in sheep.The screening of candidate genes related to sheep carcass fat and significantly related SNP sites can provide new insights for elucidating the genetic mechanism of sheep tail fat,and provide a new direction for the genetic improvement of Kazakh sheep,a local sheep breed in Xinjiang.The breeding of tail sheep provides a theoretical reference.