A TWIN-PRONGED ATTACK ON COMPLEX TRAITS

Before one starts the hunt for quantitative trait loci (QTLs) for a co mplex trait, it is necessary to show that the trait is genetically inf luenced. This evidence is most likely to come from the classical twin study-the demonstration that monozygotic twins are more similar for th e trait than dizygotic twins. The strengths and weaknesses of twin stu dies are discussed, and it is suggested that, far from becoming irrele vant with advances in molecular biology, they can improve the efficien cy of QTL detection and play an important role in unravelling developm ental genetic mechanisms.