The timing of lethality caused by homozygosity for a null allele of the epidermal growth factor receptor (Egfrtm1Mag) in mice is strongly dependent on genetic background. Initial attempts to genetically map background modifiers using Swiss-derived, outbred CD-1 mice were unsuccessful. To investigate the genetic architecture contributing to survival of Egfrtm1Mag homozygous embryos, the genetic ...

T IS almost axiomatic in studies of developmental genetics that the action I of a particular gene cannot be described completely without reference to the residual genotype or “general genic environment” (term proposed by TSCHETWERIKOFF 1926). It is also generally agreed that “all factors probably partake of the nature of modifiers, since each factor appears to affect many characters and to alte...