A developing amphibian, approx. 4 weeks old, has no forebrain development and is absent of adhesive glands, explain the following observations:
a. Goosecoid RNA injected into the two ventral blastomeres causes a secondary axis to form.
b. Injection of noggin mRNA into 1-celled UV irradiated embryos rescues the UV phenotype and embryos develop normally.
c. Injection of cerberus mRNA into the vegetal ventral blastomere of a 32-celled embryo causes a second head to form.