Mouse hepatitis virus type 4 (JHM strains). induced fatal central nervous system disease. I. genetic control and murine neuron as the susceptible site of disease

To study the dominance and number of genes controlling resistance to MHV-4, we inoculated MHV-4 intracerebrally into BALB/c (susceptible) mice, SJL/J (resistant) mice, their Fz and (35) . F2 hybrids, and the FI backcross to resistant and susceptible parents. As seen in Table II , the F1 hybrids were as susceptible to acute encephalitis as the BALB/c parents. All F1 hybrids inoculated with 100 BALB/c LDs0 died, thus indicating that resistance is recessive. Among mice bred by mating F× hybrids to each parental stock, offspring of FI mice crossed with susceptible BALB/c partners had a mortality rate of 96% as compared with a 45% mortality rate in mice parented by Fl mice crossed with SJL/ J mice. These values obtained experimentally are close to the theoretical values of 100% and 50%, respectively, that should hold true if resistance is inherited as a single recessive gene. Similarly, the mortality of F2 mice was 65%, close to the theoretical value of 75% for a one-recessive-gene model.