Genetic analysis of isolation-induced aggression in the mouse. III. Classical cross-breeding analysis of differences between two closely related inbred strains.

In two preceding papers we reported on two closely related inbred mouse strains, ABG and AB@Halle that display very large differences in isolation-induced intermale aggression. In the present article we investigated animals from a complete Mendelian cross between these strains to test the hypothesis that the behavioral difference is due to genetic variation at only a few loci, possibly only one. In the quantitative-genetic analysis of generation means and variances for the behavioral variables analyzed, relatively simple models were found. As epistasis was present in some cases, the monogenic hypothesis could not be confirmed. Also, the analysis of the segregating generations by means of Collins' nonparametric method revealed significant deviations of observed from expected distributions. We conclude that differences at more than only one single locus are correlated with the behavioral difference.