**2.1 Mice**

B6 and C3H mice were purchased from the Jackson Laboratory (Bar Harbor, Maine) and bred in our facilities. All mice were housed in plastic cages on corncob bedding (Bed O'Cobs, Anderson Cob Division, Maumee, OH), fed Purina 5020 diet (9% fat; St. Louis, MO), and given acidified tap water *ad libitum*. Mice were inspected daily and weighed monthly.

Lines derived from the B6.C3H-Ch1 recombinant strain (Bilger et al., 2004) were generated as follows. B6 females were mated with B6.C3H-Ch1 males heterozygous for the congenic region. Markers between *D1Mit285* and *D1MIT17* were used to identify recombinants, and breakpoints were mapped more finely with additional markers. Males and females from a given recombinant line were then intercrossed to generate homozygotes. Heterozygous or homozygous mice were mated with B6 to generate heterozygous experimental progeny (Figures 1 and 3, and Table 3) or homozygotes were intercrossed to generate homozygous experimental progeny (Tables 1 and 2). Tested parental B6.C3H-Ch1 were homozygous.

Lines derived from B6.BR-Ch1 were generated by mating B6 females with B6.BR-Ch1 males heterozygous for the congenic region. The markers *D1Mit143*, *D1Mit17*, and two additional microsatellite markers at 172.9 and 176.9 Mb were used to identify recombinants. (The lack of SNPs or SSLPs between B6 and BR in this region prevented refinement of these breakpoints.) Heterozygotes were intercrossed to generate homozygous lines. B6 females were then crossed with homozygous congenic males to generate experimental progeny.

The C3H.B6-Ch1 line carrying B6 alleles for distal Chromosome 1 on a C3H genetic background was generated by crossing C3B6F1 (N1) mice with C3H mice and selecting C3H.B6 N2 mice carrying B6 alleles at *D1Mit143*, *D1Mit15*, *D1Mit166*, and *D1Mit461*. Backcrossing to C3H and selection of these B6 alleles was continued for eight additional generations to generate C3.B6(*D1Mit143-D1Mit461*)N10, or "C3H.B6-Ch1" (Figure 3) mice.
