Fig. 7. Notch ligand density and N1::cre genetic mapping. A hypothetical model to explain the relationship between the strength of Notch signaling and fate mapping as a function of ligand concentration. The probability of identifying a marked lineage in tissues within N1::cre mice is correlated with Notch1 function as revealed by loss-of-function phenotypes and the ability to detect activated Notch1 protein by immunostaining (see Table 1).