Quantitative Trait Loci Mapping in Merino Sheep and Effect of Accuracy of QTL Parameter Estimation on Marker Assisted Selection

Abstract

The objectives of this thesis were to perform a genome scan for important production traits in Australian Merino sheep and to investigate issues related to the prediction of marker assisted selection (MAS) response in single and multiple trait selection schemes in animal breeding programs. In the first experimental chapter, a genome scan was performed for 4 growth and 7 fleece traits in Australian Merino sheep. Quantitative trait loci (QTL) parameters were estimated through single QTL interval mapping within and across four paternal half-sib families. The genome scan yielded 21 significant QTL for all traits at the 1% chromosome wise significance threshold level in within family analysis. Across family analysis supported most of the highly significant results from single family analysis but did not show any common significant QTL at the 1% chromosome wise significance threshold level across all families. Because of the relatively small progeny group sizes the power and the precision of the analysis are probably low and the QTL allele substitution effects are overestimated. In the subsequent three chapters some important issues related to the application of QTL information in MAS, including efficient prediction of MAS response and effect of the accuracy of estimated QTL effect in single and multiple trait selection, were investigated.