Selective breeding has been an effective tool for detecting genetic correlations between different phenotypes. For example, Metten et al. (1998) reviewed evidence from several studies showing that alcohol preference drinking and withdrawal severity in physically dependent mice are inversely genetically correlated: thus, high preferring genotypes are genetically predisposed to show low withdrawal severity and vice versa. Precisely which genes are responsible for the negative genetic correlation are unknown. Using short-term selective breeding for each of the two traits starting from a heterogeneous stock (derived from a cross of four inbred strains, including C57BL/6J and DBA/2J), Hitzemann et al. (2009) found seven QTLs that affected both traits in the expected inverse direction, and offered a number of plausible candidate genes worthy of further investigation.
