Level and shape of sequences of motor behavior in inbred and hybrid mice

Three-hundred seventy-five mice of six inbred strains and their F1 hybrid crosses were observed in a barrier apparatus. Frequencies of jumping over barriers were recorded at each of ten 30-sec intervals. Graphs plotted of mean jumps at each time point show several F1 curves with an apparently adaptive pattern: low frequencies of jumps at start, gradually rising, then leveling off. Nine out of 15 F1 curves also show evidence of heterosis: jumping frequencies of hybrids exceed those of parent strains. Lack of heterosis was peculiar to crosses in which C57BL/6 was one of the parents. A coefficient of convexity C was developed to quantify the shapes of the temporal patterns of proportions of animals engaged in jumping at a given point in the sequence. F1 curves (unlike inbred strains) were found, on the whole, to be negatively convex.