Maternal effects on mouse brain weight.

When BALB/cCF mice were crossed reciprocally with 4 other inbred strains, adult brain weights averaged 21.0 mg heavier for hybrid offspring with a BALB mother than those with a BALB father. Reciprocal backcrosses to BALB revealed that this effect was a consequence of the BALB maternal environment, not cytoplasmic or sex chromosomal influences. These findings demonstrate that BALB mice have heavier brains than those of several other inbred strains, partly because of chromosomal influences, but also because of their maternal environment, an environmental influence which usually functions as a component of heredity in studies comparing inbred strains. Backcrosses also revealed a maternal environment effect whereby offspring with an F1 hybrid mother had adult brains averaging 9.0 mg heavier than those with a BALB mother.