COMBINED GENETIC AND PHYSIOLOGICAL ANALYSIS OF A LOCUS CONTRIBUTING TO QUANTITATIVE VARIATION

The natural variation of many traits is controlled by multiple genes, individually referred to as quantitative trait loci (QTL), that intera ct with the environment to determine the ultimate phenotype of any ind ividual. A QTL has yet to be described molecularly, in part because st rategies to systematically identify them are underdeveloped and becaus e the subtle nature of QTLs prevents the application of standard metho ds of gene identification. Therefore, it will be necessary to develop a systematic approach(es) for the identification of QTLs based upon th e numerous positional data now being accumulated through molecular mar ker analyses. We have characterized a QTL by the following three-step approach: (1) identification of a QTL in complex populations, (2) isol ation and genetic mapping of this QTL in near-isogenic lines, and (3) identification of a candidate gene using map position and physiologica l criteria. Using this approach we have characterized a plant height Q TL in maize that maps to chromosome 9 near the centromere. Both map po sition and physiological criteria suggest the gibberillin biosynthesis gene dwarf3 as a candidate gene for this QTL.