Inheritance of susceptibility to friend mouse leukemia virus. VII. Establishment of a resistant strain

Based on the previous observation that a single major autosomal locus controls susceptibility to Friend leukemia virus in mice, an attempt was made to place the gene for resistance, Fv r , from resistant C57Bl/6 mice into the genetic background of susceptible D D D mice. The cross‐intercross system was adopted for this purpose, the mice with Fv r /Fv r genotype being selected by progeny test at each even‐numbered generation. During successive matings, the effect of gene Fv r was not diluted out, and progeny were almost always obtained as expected from the single gene hypothesis. After five to six cycles of cross‐intercross, brother‐sister mating was done between the mice with Fv r /Fv r genotype. The progeny are homozygous for gene Fv r and could be assumed to be congenic with D D D mice except for susceptibility to Friend leukemia virus. In the mice of this strain, the virus does not induce typical splenomegaly, but multiplies to a considerable level. It could therefore be concluded that the locus Fv is involved rather in cell proliferation than in virus multiplication.