Preliminary results corroborating the polygenic control of immunological tolerance.

Tolerance-susceptible (TS) and -resistant (TR) lines of mice are in the process of bidirectional genetic selection starting from a genetically heterogeneous population achieved by the equilibrated intercrossing of eight inbred lines. Mice are intragastrically pretreated and then immunized with hen ovalbumin or bovine serum albumin and the extreme phenotypes are selected for assortative mating. The normal distribution of agglutinin titers in the F0 population and the significant interline difference already observed in the F2 and F3 generations indicate that oral tolerance is a character controlled by the additive effect of several independent loci. The mean heritability (h2) obtained thus far is 11% for the TS line and 19% for the TR line.