ABSTRACT
This chapter reviews quantitative trait loci (QTL) mapping in outbred pedigrees: the influence of life history attributes, terminology and concepts unique to outbred QTL mapping, general pedigree designs, and the basics of QTL analyses. QTL mapping for outcrossed pedigrees is complicated by the absence of complete homozygosity in the parents. The longevity of perennials means that all three generations required for some QTL mapping designs may be living at the time that QTL mapping is conducted. Phenotypic data often accumulate on each plant over decades, adding a temporal complexity to QTL mapping. Genetic load tends to be higher for outcrossing perennial plants than for other plants and animals, making related matings, inbred lines or nearly isogenic lines unavailable. In the case of forest trees, QTL effects must be detected in mature trees if the trait has economic importance at harvest. Many perennial plants have delayed onset of reproduction, slowing the creation of large, informative pedigrees and advanced generations of crosses.
