Fig. 10. Schematic for the patterning of rhombomeres 1-6 in the hindbrain in various loss of function (LOF) combinations of Hox PG1 genes, and also the Hox cofactor Pbx. There is a successive loss of rhombomeric identity as more PG1 function is removed in the different organisms: zebrafish (McClintock et al., 2002); mouse (Rossel and Capecchi, 1999); and Xenopus (this study). The triple PG1 LOF phenotype in Xenopus resembles the Pbx complete LOF in zebrafish (Waskiewicz et al., 2002).