Practice question

Formation of a complete pluteus larva from a single isolated blastomere of a four-cell stage sea urchin embryo demonstrates classical conditional, regulative development. Fate is not prefixed by inherited determinants; instead, blastomeres continuously interpret positional information through Delta-Notch, Wnt/beta-catenin and Nodal signaling, adjusting lineage allocation to replace missing cells. Such compensation via community effect ensures robustness and whole-embryo regeneration from partial embryos. By contrast, mosaic embryos produce only partial structures upon blastomere isolation. Sea urchin results, pioneered by Hans Driesch, founded the concept of potency exceeding fate.