Genome-wide Association Study And Selection Signatures Detection On Traits Of Fat Deposition In Hulun Buir Sheep's Tails

Through the long process of natural and artificial selections,sheep have obtained the unique characteristic of depositing fat in their tails.Similar to the camel's hump,fat in sheep tails can provide energy to ensure their survival in harsh environment.To uncover the genetic mechanism,we selected300 Hulun Buir sheeps with two types of fat tails,and 150 individuals were selected in each line.Genome-wide association studies?GWAS?on traits of fat deposition and body sizes in Hulun Buir sheep were carried out using the Ovine Infinium HD SNP BeadChip genotypes.Selection signature detection was performed in the same population.This study aims to use the two methods to identify relevant candidate genes controlling fat deposition in sheep tails.The specific contents are as follows:?1?The GWAS was carried out by a linear mixed model and binary trait analytical model with an R package GenABEL.Two kinds of mixed models were employed to analyze ten traits,including body slanting length?BL?,height?HT?,chest girth?CG?,tail length?TL?,tail width?TW?,tail circumference?TC?,carcass weights?CW?and fat weights of tails?TF?,ratio of CW to TF?RCT?and types of tails?TT?.Results showed that 1,17,9,24 and 14 SNPs were identified in RCT,TF,TW,TT and CG,respectively.Five common SNPs were identified in TF and TW.These SNPs were located in 87 genes regions.Of them,20 genes were associated with fat metabolism,such as ACSL5,ACOX1,AKT2,DGAT1,RASA2,ADRB3,DGAT2,NAPG,PHYH and so on.In addition,three genes identified were associated with body sizes,including GFI1B,TGS1 and TMEM68.?2?The whole-genome single locus F_STT values were calculated to detect the selection signature from two lines of Hulun Buir sheep with different tail types,based on the Ovine Infinium HD SNP BeadChip genotypes chip.The cubic smoothing spline method was defined the numbers and sizes of variable windows.Then,the W statistic was performed to detect the windows with selection signature to identify selected segments and annotate related genes.27 of variable windows reached a very significant level?P<0.001?.After annotation,these windows harbored 337 candidate genes,of which 22 were related to the fat metabolism,such as ACOX1,RYR3,AKT2,FADS1,ABCG1,ACADSB,UCP2,TMEFF2 and so on.Through GO analysis,these candidate genes were mainly enriched in the intracellular part,organonitrogen compound metabolic process and small molecule metabolic process.?3?Three genes of AKT2,ACOX1 and RYR3 were identified by two methods.Therefore,these three genes could be used as the best candidate genes to identify tail type trait.The results of this study can provide a theoretical foundation for further exploring the molecular mechanism of fat deposition in tail,the breeding of Hulun Buir sheep and the preservation of economically important traits.