One strategy for QTL confirmation uses congenic mice that are entirely C57BL/6J in genotype with the exception of a region on a single chromosome from the DBA/2J genotype or vice versa. This approach was used by Blizard and McClearn (Blizard and McClearn 2000) to substantiate the genetic association of ethanol and sucrose intake. We have tested two chromosome 2 congenics vs their matched C57BL/6J and DBA/2J background mice. The background strain mice were originally obtained from The Jackson Laboratory, and then used for the backcrossing required to create congenics (Bennett 2000), and bred alongside the congenics during the same time span. Adult mice were tested in a 24-h choice procedure for their consumption and preference for a 10% (v/v) ethanol solution when offered vs water, using methods for measuring consumption that are standard in our laboratory (Phillips et al. 2005). The 10% ethanol solution was offered for 4–10 days. As shown in the left panel of Fig. 1, chromosome 2 congenic data supported QTL capture on the C57BL/6J background (introgression of the DBA/2J region reduced ethanol consumption), but not on
