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1、Confirmed linkage for QTLs affecting muscling in Texel sheep on chromosomes 2 and 18,G.A.Walling,P.M.Visscher,G.Simm&S.C.BishopRoslin Institute(Edinburgh)University of EdinburghScottish Agricultural College,2,Project Aims,Started July 1999Detect and verify QTL for growth and carcass traitsInvestigat
2、e genotyping strategies,http:/www.roslin.ac.uk/sheepmap,3,Aims,Use commercial UK Texel sheepUse candidate regions to Determine evidence for major genes:Chromosome 2Chromosome 18,4,Scientific Background,Studies in Belgium,Australia and New Zealand suggest a major gene for muscling and fatness on chro
3、mosome 2Putative Callipyge and Carwell loci both increase muscling and are located on chromosome 18,5,Animals,Five large half-sib families1999:348 progeny2000:275 progenyBlood collected from all rams and progenyDNA extracted from blood,6,Phenotypic Traits,8 Week Weight(8WW)Weight at ultrasonic scann
4、ing(ScanWT)Ultrasonic Muscle Depth(Mus)Ultrasonic Fat Depth(Fat)Muscle Depth adjusted for weight(MusWT)Fat Depth adjusted for weight(FatWT),7,Genotyping,All 5 sires screened for:28 markers on chromosome 214 markers on chromosome 18Progeny genotyped for markers heterozygous in their sire,8,Linkage Ma
5、ps,Produced using Cri-MapFinal maps in good agreement with previous studies,9,Statistical Analysis,Traits corrected for fixed effects and covariates:estimated using ASREMLInheritance probabilities calculated at 1cM intervalsRegress adjusted phenotypes on inheritance probabilitiesat each locationfor
6、each family,10,Thresholds and Further Analyses,Nominal P-value of 0.01:Lander&Kruglyak(1995)Significant results:Compare with a 2 QTL model using grid search methodConfidence intervals using bootstrapping,11,Results:Chromosome 2,Significant effects clustered around two regions:Fat traits around 170cM
7、Muscle traits around 65cMBest model for weight traits was a QTL in each of these two regions:P(2QTL vs.1QTL)0.05,12,Chromosome 2:Fat Traits,13,Chromosome 2:Muscle Traits,14,Chromosome 2:Weight traits,15,Chromosome 18:Results,All results highlight one region affecting muscle and fatness95%CI include
8、Callipyge and Carwell loci,16,Chromosome 18:Results,Callipyge Locus,17,Results:Effects,Given in phenotypic standard deviationsAfter removing fixed effects and covariatesChromosome 2Fat:0.66Muscle:0.618WW:0.75ScanWT:0.69Chromsome 18Muscle:0.59Fat:0.60,18,Conclusions,Candidate region approach successf
9、ulIdentify loci in unrelated populationsBeneficial approach when other methods are unavailable,19,Conclusions,Best explanation for chromosome 2 is 2 QTLs:65cM muscle growth170cM fat growthRegion on chromosome 18 affecting muscle and fat,20,Chromosome 18:Callipyge or Carwell?,Position almost identica
10、l to both lociEffects similar to Carwell not CallipygeCarwell not previously known to affect fatness:Closely link locus affecting fatnessAlternative Carwell allele affecting fatness,21,Future Goals,Improve estimate of position and effectsIncrease numbers by:Collecting from more progenyWiden the study to other familiesUltimate goal to identify the Carwell locus,22,Acknowledgements,The UK sheep genome mapping project is funded by:,
