Fig. 1: Major components of a QTL study. Recall from the previous lesson that the objective of QTL analysis is to locate and characterize genetic factors that influence quantitatively inherited traits, i.e., those that are controlled by a few to many genes acting together to produce a phenotype. The basic outline of a QTL study is shown in Fig. 1. Steps 1, 2, and 3 were covered in QTL Analysis 1; this lesson will cover step 4.