What hope is there for dissecting the genetic basis of variation of quantitative traits?
In the past 20 years, there has been a shift from optimism to pessimism. At first, it seemed possible that QTL mapping could identify something like several to tens of loci with alleles of moderate to large effect that could explain quantitative traits and complex diseases. Latterly, it has become clear that the task will be to identify unambiguously hundreds of genes with alleles with small effects affecting any one trait, and success seems more remote. The challenge becomes particularly arduous given context-dependent effects and the prospect of drilling down from QTL region to candidate gene one QTL at a time. Several recent technical developments offer the hope of overcoming the difficulties, however. Two major obstacles have been the need for a dense panel of molecular markers for high-resolution mapping in the organism of interest, and for a way of genotyping these markers economically and in parallel in tens of thousands of individuals. Nextgeneration sequencing methods make pos
