The studies in this thesis describe the application of genotyping and allele specific expression analysis to genetic studies. The role of the gene NPC1 in Triglyceride metabolism was explored in mouse models and in humans on the population level in study I. NPC1 was found to affect hepatic triglyceride metabolism, and to be relevant for controlling serum triglyceride levels in mice and potentially in humans. In study II the utility of the HapMap CEU samples was investigated for tagSNP selection in six European populations. The HapMap CEU was found to be representative for tagSNP selection in all populations while allele frequencies differed significantly in the sample from Kuusamo, Finland. In study III the power of Allele specific expression as a tool for the mapping of cis-regulatory variation was compared to standard eQTL analysis, ASE was found to be the more powerful type of analysis for a similar sample size. Finally ASE mapping was applied to regions reported to harbour long non-coding RNAs and associated SNPs were compared to published trait-associations. This revealed strong cis-regulatory SNPs of long non-coding RNAs with reported trait or disease associations.