ABSTRACT
This chapter addresses the molecular cloning of individual genetic determinants for which allelic variation does not result in discrete phenotypic classes in the primary mapping population where the variants are discovered. Cloning of the first Quantitative Trait Loci (QTL) may not be the hardest one – rather, it may be the most fortuitous one, and the technological difficulty of this goal may be reflected by the overall frequency of failures rather than by the achievement of a few successes. High-priority candidate QTLs might be chosen based on economic or medical importance, evolutionary significance as reflected by apparent correspondence across diverse taxa, or simply based on falling at well-characterized locations in genomes that are facile models. The ability to assemble groups of desirable QTL alleles into cassettes that might be integrated into a plant or animal genome as an artificial chromosome would enable one to avoid the necessity of dealing with many independently-segregating loci – rendering complex traits discrete.
