Tagging for QTLs - The polygenic traits, controlled by quantitative trait loci, are characterized by a continuous range of variation. The plants at the two extremes of this range should differ at most loci controlling a particular trait. These two extremes may be classified in corresponding groups and two DNA samples from these bulked plants may be screened for RAPDs using a number of random primers for PCR.
Thus the markers linked to loci controlling a particular quantitative trait can be identified. For this approach, if recombinant inbred lines (RILs) or doubled haploids (DHs) are used, this will greatly facilitate tagging of QTLs.
RILs and DHs can also be grown in replicated trials at different locations for several years to partition heritable and non heritable variation, so that markers linked to heritable loci showing minimum G x E (genotype X environment) interaction are identified. This approach using RFLPs has already been utilized in several crops- and will be utilized in future with the help of RAPDs.