ABSTRACT
The development of ubiquitous polymorphic genetic markers that span the genome have made it possible for quantitative and molecular geneticists to investigate what M. D. Edwards et al. referred to as the numbers, magnitudes, and distributions of quantitative trait loci (QTL). QTL are identified as significant statistical associations between genotypic values and phenotypic variability among the segregating progeny. Magnitude of QTL effects are reported as the minimum and maximum percent of phenotypic variability explained by the significant QTL. Genomic locations of the QTL with estimated large effects mapped to syntenic regions across all three genera. Identification of QTL for agronomically important traits has been pursued through progeny derived from intraspecific crosses of adapted inbred lines. There is a tendency to make the inferential leap from QTL to physiology of gene effects at genetic loci, but QTL are, by definition, merely significant statistical associations.
