Finding the molecular basis of quantitative traits: Successes and pitfalls

Understanding the molecular basis of quantitative genetic variation is a pr incipal goal for biomedicine. Although the complex genetic architecture of quantitative traits has so far largely frustrated attempts to identify gene s in humans by standard linkage methodologies, quantitative trait loci (QTL ) have been mapped in plants, insects and rodents. However, identifying the molecular bases of QTL remains a challenge. Here, we discuss why this is a nd how new experimental strategies and analytical techniques, combined with the fruits of the genome projects, are beginning to identify candidate gen es for QTL studies in several model organisms.