1) Explain how the interactions between dorsal, dpp, and sog establish the Dorsal-ventral pattern of a Drosophila embryo. How is this similar to how BMP4, chordin and noggin pattern the developing mesoderm in a Xenopus embryo?

2) Explain how the AER and ZPA pattern the developing limb bud.

3) Compare the role of hedgehog signaling in patterning the segments in Drosophila embryos with the role of Shh in patterning the neural tube in vertebrates.

4) How do Pax6, Olig2 and Nkx2.2 maintain the DV patterning of the neurotube?

5) Describe the reciprocal interactions between the developing lens placode and the optic vesicle from the brain.