[The genetic architecture of emotionality in rats using Mendelian cross analysis]

Two inbred strains of Tsukuba Emotionality Rat (THE and TLE) and four hybrids derived from them were observed for ambulatory response in a novel environment as a measure of emotionality. The Runway Test (modified "timidity test") was run for successive three days. Mean transformed (square root) scores of ambulation for generation were subjected to Mendelian cross analysis. Total ambulation scores showed significant additive genetic effect, maternal effect and environmental effect. Directional dominance toward low level of response was present only for males. Daily ambulation scores showed changes in the genetic architecture over three days and the difference between males and females. For females, directional dominance occurred toward low level on Day 1, toward high level on Day 3, but no directional dominance was observed on Day 2. Males' directional dominance toward low level, on the other hand, declined with days. These findings on the genetic architecture of emotionality were discussed with reference to evolutionary adaptation.