QTL Detection in the UK Suffolk and Texel Sheep Sire Referencing Schemes

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QTL Detection in the UK Suffolk and Texel Sheep
Sire Referencing Schemes

• G.A. Walling, A.D. Wilson, B.L. McTeir, P.M.
  Visscher, G. Simm S.C. Bishop

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Introduction

• Detecting Quantitative Trait Loci (QTL) provides
  tools for
• Enhancing Genetic Progress
• Improving Biological Understanding

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QTL detection in UK sheep

• Utilise structure of terminal sire reference
  schemes (SRSs)
• Texel
• Suffolk
• Ideal for studying segregation of major genes

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Segregation of a Major Gene
X
AB
CC
CC
BC
AC
AC
BC
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Aim

• To identify QTL for performance traits in
  commercial Suffolk and Texel sheep

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Methods

• Blood Samples from large half-sib families
• Three Suffolk
• Five Texel
• Genotyped for up to 9 candidate regions of the
  genome

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Regions Used
4 Leptin
1 Growth in Cattle
5 Calpastatin
2 Myostatin
3 IGF1 INFG
6 Growth in Sheep Cattle
11 Growth Hormone 1
18 Callipyge Carwell
20 MHC Region
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Phenotypic Traits

• 8 Week Weight (8WW)
• Weight at ultrasonic scanning (ScanWT)
• Ultrasonic Muscle Depth (Muscle)
• Ultrasonic Fat Depth (Fat)
• Muscle Depth adjusted for weight (MusWT)
• Fat Depth adjusted for weight (FatWT)

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Statistical Analysis

• Traits corrected for fixed effects and
  covariates
• ASREML
• QTL Express mapping software

http//qtl.cap.ed.ac.uk/
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Results

• Significant effects on chromosomes 1, 2, 3, 4, 18
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• 1 Nominal significance level
• Effects on 2 18 supported by 2 or more sires

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Chromosome 2
Myostatin
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Results Effects

• Fat 0.6mm
• Muscle 1.2mm
• ScanWT 1.9 2.8 kg
• Explain 6-12 phenotypic variance

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Chromosome 18 Results
Callipyge Locus
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Results Effects

• Muscle 1.8mm
• Fat 0.8mm
• Explain 13 and 9 phenotypic variance
  respectively

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Chromosome 18 Callipyge or Carwell?

• Position almost identical to both loci
• Effects similar to Carwell not Callipyge
• Carwell not previously known to affect fatness
• Closely link locus affecting fatness
• Alternative Carwell allele affecting fatness

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Conclusions

• Candidate region approach successful
• Identify loci in unrelated populations
• Beneficial approach when other methods are
  unavailable

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Conclusions

• Best explanation for chromosome 2 is 2 QTLs
• 65cM muscle growth
• 170cM fat growth
• Region on chromosome 18 affecting muscle and fat

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Future Goals

• Improve estimate of position and effects
• Increase numbers
• Progeny
• Families
• Breeds
• Ultimate goal to identify the Carwell locus

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Acknowledgements

• The UK sheep genome mapping project is funded by