Abstract
Many mice of the inbred strain BALB/cCF have deficient corpus callosum, and a few of them have total absence of this large forebrain commissure. Reciprocal F1 hybrid crosses with the inbred strains A/J, C57BL/6J, and DBA/2J revealed that inheritance of the defect is completely recessive. Reciprocal backcrosses to BALB/cCF revealed that inheritance is not attributable to a single Mendelian locus with the same degree of penetrance as in the parent strain. The ac locus has not been rediscovered. Instead, there is good reason to withdraw ac from current listings of Mendelian loci in the mouse.