Segregation of splenomegaly in F2 mice derived from BXH-2. F1 and F2 animals derived from (BALB/cJ × BXH-2) and from (A/J × BXH-2) crosses were killed and spleen index was calculated as described in “Materials and methods.” For individual F2 crosses, mice were further separated according to homozygosity or heterozygosity for C57BL/6J (B6), BALB/cJ (BA), or A/J (A) alleles at D8Mit13 (polymorphic with BALB/cJ) or D8Mit14 (polymorphic with A/J). BXH-2 is fixed for B6 alleles at D8Mit13 and D8Mit14. Dots represent individual mice, and means for each group are shown as lines on the graphs.