A Few Questions for Thought Integrate the contributions of mosaic and regulatory mechanisms in Xenopus. What is a fate map and how is it applied to metazoan development? Compare and contrast fate maps for our different model organisms. Describe the molecular bases of inductive signaling via the TGF-Beta and Wnt pathways. What is the gray crescent, how is it formed and what does it mark? Using your understanding of METRO, suggest an hypothesis for how the gray crescent determines the fate of cells that ultimately inherit this cytoplasm. Describe the process of gastrulation in Xenopus and the contributions of each of the three key tissue layers to the development of the tadpole body.