Brain weight changes resulting from enriched rearing conditions: A diallel analysis

Housemice from 6 inbred lines and their F 1 crosses were reared in standard or enriched laboratory cages. A genetic analysis of brain and body weights indicated a significant directional dominance effect toward larger brain in F 1 crosses among enriched animals only, even when adjustments for body weight were made. The proportion of additive genetic variance was greater in standard caged animals than in enriched animals. Maternal effects played a small but significant role in influencing brain weights apart from those indirectly caused by body weight effects. The use of laboratory reared animals for genetic studies is questioned when environmental influences are known to have a strong effect on the character being studied, and the results are to be used to make inferences concerning the adaptive significance of the character.