The quantitative increase in locomotor activity and decreased body weight of Lightweight mutants could arise from or be influenced by other ENU-induced point mutations or polymorphic differences between the B6 and D2 strains. Thus, several experiments were performed to further explore these possibilities. First, a ∼1.4 Mb region surrounding the Lightweight mutation was introgressed fully onto the C57BL/6J genetic background to create the B6.D2-Unc79Lwt (Lwt) congenic (see Figure 2). We confirmed the uniformity of the background by genotyping against a panel of 555 informative SNPs spaced evenly across the genome [24].
