Quantitative trait (QT) is a terr. ~ of central importance in the fields of biology and agriculture. As the term indicate~, QT refers to characters that can be measured on a quantitative scale. This is, however, a textual definition but we also need a scientific one. Such a definition would necessarily be with reference to the field or activity in which QT is to be employed. Therefore we restrict our attention to
agriculture, and more specifically to crop breeding and improvement.