title: Imputation-Based Fine-Mapping Suggests That Most QTL in an Outbred Chicken Advanced Intercross Body Weight Line Are Due to Multiple, Linked Loci.
abstract: The Virginia chicken lines have been divergently selected for juvenile body weight for more than 50 generations. Today, the high- and low-weight lines show a >12-fold difference for the selected trait, 56-d body weight. These lines provide unique opportunities to study the genetic architecture of long-term, single-trait selection. Previously, several quantitative trait loci (QTL) contributing to weight differences between the lines were mapped in an F2-cross between them, and these were later replicated and fine-mapped in a nine-generation advanced intercross of them. Here, we explore the possibility to further increase the fine-mapping resolution of these QTL via a pedigree-based imputation strategy that aims to better capture the genetic diversity in the divergently selected, but outbred, founder lines. The founders of the intercross were high-density genotyped, and then pedigree-based imputation was used to assign genotypes throughout the pedigree. Imputation increased the marker density 20-fold in the selected QTL, providing 6911 markers for the subsequent analysis. Both single-marker association and multi-marker backward-elimination analyses were used to explore regions associated with 56-d body weight. The approach revealed several statistically and population structure independent associations and increased the mapping resolution. Further, most QTL were also found to contain multiple independent associations to markers that were not fixed in the founder populations, implying a complex underlying architecture due to the combined effects of multiple, linked loci perhaps located on independent haplotypes that still segregate in the selected lines.
authors: Department of Medical Biochemistry and Microbiology, Uppsala University, 751 23 Sweden.
authors: Monika
authors: M
authors: Brandt
authors: Division of Computational Genetics, Department of Clinical Sciences, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden.
authors: Muhammad
authors: M
authors: Ahsan
authors: Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061.
authors: Christa F
authors: CF
authors: Honaker
authors: Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061.
authors: Paul B
authors: PB
authors: Siegel
authors: Department of Medical Biochemistry and Microbiology, Uppsala University, 751 23 Sweden orjan.carlborg@imbim.uu.se.
authors: Örjan
authors: 0000-0002-2722-5264
authors: Ö
authors: Carlborg
mesh_terms: D000818:Animals; D001835:Body Weight / Q000235:genetics*; D002645:Chickens / Q000235:genetics* / Q000254:growth & development; D002874:Chromosome Mapping; D003433:Crosses, Genetic; D014644:Genetic Variation; D005838:Genotype; D006239:Haplotypes; D010375:Pedigree; D010641:Phenotype; D040641:Quantitative Trait Loci / Q000235:genetics*
keywords: QTL fine-mapping; Virginia chicken lines; advanced intercross body weight line; imputation-based association