Figure 1

SWR/J female mice were crossed to male mice belonging to one of the 13 CXB RI strains to obtain a population of 376 male and female (SWR/J x CXBN)F1 mice. For every locus, each F1 mouse received one copy of the SWR/J allele (white bars) and one copy of the CXBN allele (orange and black bars). Therefore, heterozygosity resulted at every genetic locus, with one allele derived from the SWR/J strain (white bar) and the other derived from either the BALB/c strain (orange band) or the C57BL/6 strain (black band).