The Genetic Architecture of Complex Traits in Sheep

Abstract

Many important traits in biology, medicine and agriculture are complex and quantitative in that they exhibit continuous variation and non-trivial patterns of genetic inheritance. They are largely polygenic and influenced by factors such as gene-gene and gene-environment interactions. Important reasons to study complex traits include trying to understand how the genetic components operate on their own and how they relate to each other, quantification of the contributions of these elements to trait variation, and elucidation of the underlying genetic architecture behind a trait. An understanding of the sources and consequences of variation in complex traits and identification of the genes involved provides us with a handle to manipulate biological systems, which can have direct applications in medicine and agricultural production. From an agricultural standpoint there are huge economic benefits to be achieved by a better understanding and exploitation of the genetic architecture of complex production traits such as milk yield in dairy animals and meat quality in e.g. sheep or cattle. This thesis is centred on making some inroads to better understand the genetic architecture of complex traits in sheep. The thesis progresses through a characterization of genetic structure and variability in Australian sheep populations, followed by a genome-wide association study for weight. Then a novel approach to improve estimates of genomic breeding values is discussed. Lastly, the inheritance and partitioning of gene expression variance is studied. A more detailed breakdown of the thesis follows.