A locally congenic backcross design in pig: a new regional fine QTL mapping approach miming congenic strains used in mouse.

Juliette Riquet,Denis Milan,Jean-Pierre Bidanel,Nathalie Iannuccelli,Helene Gilbert,Bertrand Servin,Yvon Billon,Marie-Pierre Sanchez

doi:10.1186/1471-2156-12-6

Abstract

BackgroundIn previous studies, a major QTL affecting fatness and growth has been mapped to pig chromosome 1q (SSC1q) using Large White - Meishan intercrosses. A higher fat depth and a larger growth rate have been reported for the allele of MS origin. Additionally the LW allele showed partial dominance effects over the MS allele for both traits. In order to refine the QTL mapping interval, advanced backcross generations were produced. Recombinant heterozygous sires were mated to LW sows in order to progeny test the sire segregation of the QTL and refine the QTL localisation. However due to the partial dominance of the LW allele, BC scheme using LW as the receiving population was not optimal.ResultsTo overcome the difficulties related to the dominance of the LW QTL allele, a population of dams locally homozygous for the MS haplotype in the QTL region, but with an overall 29/32 LW genetic background, has been set up. Progeny testing results, using these receiver dams, were much more significant than those previously obtained with LW dams, and the SSC1 QTL interval was refined to 8 cM. Considering the results obtained, a powerful experimental design for farm animals is proposed, mimicking locally genetically identical strains used in mouse for QTL fine mapping.ConclusionsWe have further characterized the fatness QTL on pig chromosome 1 and refined its map position from a 30 cM interval to a 8 cM interval, using a locally congenic BC design. We have obtained highly significant results and overcome difficulties due to the dominance of the LW allele. This design will be used to produce additional, advanced BC families to further refine this QTL localization.

Highlights

In previous studies, a major QTL affecting fatness and growth has been mapped to pig chromosome 1q (SSC1q) using Large White - Meishan intercrosses
Fine mapping of SSC1 QTL Quantitative trait loci with strong effects on growth and body composition were detected in an F2 cross between Large White (LW) and Meishan (MS) pigs within the French PorQTL program [8,9]
Among the significant or suggestive effects found for different chromosomal regions, a QTL with large effects on backfat thickness was located on chromosome 1, with a rather large initial mapping interval (θ = 30 cM) delimited by SW1828 and SW2512 microsatellites

Summary

Introduction

A major QTL affecting fatness and growth has been mapped to pig chromosome 1q (SSC1q) using Large White - Meishan intercrosses. The dams used are from the European parental breed because backcrosses using exotic breed (Wild Boar or Meishan) are economically difficult to sustain due to low growth rate and poor carcass quality of the animals. This strategy is based on two important assumptions. The two breeds are assumed to be each fixed for a different QTL allele (q or Q) associated with different phenotypic values If this assumption does not hold and the introgressed allele from the exotic line (say q) is still segregating in the receiving dam line used to produce the backcross, a sire may have received the same allele from the two breeds. Based on the absence of QTL segregation in the progeny, the region defined by the exotic chromosomal segment of the sire will be wrongly excluded from the QTL confidence interval

Methods

Results

Conclusion