| Recently, much studies make great effort to find possible sources underlying the so-called ’missing heritability’ evident, using genome-wide association studies (GWAS) in quantitative trait, such as human complex disease. However, solving the problem completely is a long-term and challenging task. Studying heritability of genome-wide gene expression traits can shed light on the goal of understanding the relationship between phenotype and genotype, and provide evidence to explaining the missing heritability.First of all, we give a quick overview of esearch status of genome-wide association studies, missing heritability and eQTLs in this thesis. Then, we estimate the heritability of flocculation of 294 Saccharomyces cerevisiae by Gibbs sampling, and find missing heritability in combining with study of 4 QTL major genes which have been mapping in previous experiment. Later, we try to explore the reasons of missing heritability from study in gene expression and eQTLs. So, we used microarray gene expression measurements and genome-wide SNP genotype data from 210 HapMap individuals to examine the heritability of gene expression traits. Heritability levels for expression of 8040 genes were estimated by applying variance component model analyses and 562 expression quantitative loci (eQTLs) were detected. Our results indicate that gene expression traits display a bimodal distribution of heritability, ranging from 0 to almost 100%. Higher heritability levels are shown by housekeeping genes and genes associated with cis eQTLs. Both cis and trans eQTLs make comparable cumulative contributions to the heritability. Finally, we modelled gene-gene interactions (epistasis) for genes with multiple eQTLs and revealed that epistasis was common for trans eQTLs and made a substantial contribution in explaining missing heritability. This highlights the importance of studying interaction at the gene expression level as an important source of variation underlying missing heritability. |
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