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Section 6.ppt

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Western University
Biology 3338A
Sashko Damjanovski

From one fertilized egg, need to undergo - Differentiation - Morphogenesis - Growth - Reproduction - (Evolution) Gastrulation Highly ordered cell and tissue movements occur whereby cells of the blastula are rearranged. Results in the formation of Germ Layers. Most higher phyla – 3 axes:Anterior/Posterior, Dorsal/Ventral and Left/Right - often bilateral - are triploblastic (3 germ layers) The evolution of mesoderm had important consequences on the diversity of metazoans. Sea urchins are not bilateral, but are still triploblastic Meso In the sea urchin blastula (as in others), cells are Macro already fated. Micro Micromeres are able induce ectodermal cells (mesomeres) to acquire other fates. Sea Urchin development Pgs 217-232 Micromeres can induce a secondary axis in sea urchin embryos if added to anterior regions. (competence and induction) -catenin helps specify the vegetal cells of the urchin embryo; (-catenin is stained by a fluorescently labeled antibody) B) Normal C) Expanded D) Restricted - catenin distribution Normal sea urchin development, following the fate of the cellular layers and cell movements of the blastula. Also, convergent extension convergent extension Sea Urchin Gastrulation Ingression of primary mesenchymal cells Sea Urchin gastrulation At about 1000 cells vegetal plate (VP) forms. (includes original micromeres - red) As gastrulation begins, some VP cells ingress into blastocoel and form 1º mesenchyme-blue. (subsequently, remaining VP cells invaginate forming an
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