Practice question

Proof that graded morphogen concentration determines fate came from Xenopus animal cap experiments where defined doses of recombinant Activin elicited distinct mesodermal and endodermal programs. Low Activin induced ventral mesoderm and pan-mesodermal marker Xbra, intermediate induced muscle and MyoD, high induced organizer genes goosecoid, chordin and notochord plus endoderm markers Sox17. Dose-response mirrored embryonic distribution of endogenous Activins and Nodal-related signals from vegetal hemisphere, demonstrating quantitative threshold responses and differential enhancer affinity. Griffith, Hershey-Chase, Avery-MacLeod-McCarty experiments concerned DNA as heredity material. Activin titration remains classic vertebrate morphogen demonstration linking gradient to discrete fate specification.