Scenarios proposed for the emergence of the constitutive domains of DSL ligands and Notch receptors during eukaryote evolution. These scenarios are inferred from our analyses on the basis of the phylogenetic hypotheses of Baldauf 2003  and the application of the principle of parsimony. The left and the right halves of the figure represent the two rooting hypotheses for the eukaryotes. A line represents the appearance of a domain, a cross represents the loss of a domain. Each colour corresponds to a specific domain (see figure inset). Domain presences are summarized under each taxa.