Current success in detecting complex trait loci in general, and quantitative trait loci (QTLs) using model organisms in particular, has attracted major biological and biomedical interest. The potential ability to identify genes and their function provides opportunities for new diagnostics and treatments of complex genetic dis-eases. Despite the success in gene mapping, however, cloning of complex trait loci or QTLs is not straightforward. A major obstacle lies in achieving fine mapping resolution for the detected loci. Compared to the rapid development of sophisticated statistical and molecular tools, development and analysis of experimental de-signs for various stages in OTL mapping experiments have barely been considered. In this study, novel and existing experimental strategies for OTL analysis are presented and evaluated.

A complex trait is defined as a trait in which a one-to-one rela-tionship between genotype and phenotype does not exist. Risk factors, susceptibility and most quantitative phenotypes fall into the complex trait definition. Until recently, the lack of molecular and analytical tools made the genetic analysis of complex-traits virtually impossible. With current progress, the identification of genes underlying complex traits becomes one of the major chal-lenges of genetics today.