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Animal Development

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Animal Development

  1. 1. Dr. Chambers<br />Animal Development<br />
  2. 2. I. The Stages of Early Development<br />A.Epigenesis<br />-The idea that an animal emerges gradually from a relatively formless egg<br />-Proposed by Aristotle 2,000 years before the idea of preformation embryos within embryos<br />
  3. 3. b. Fertilization<br />Acrosomal reaction<br />Sperm+Egg<br />Hydrolytic enzymes digest through material substance of cell <br />Activates egg and brings together the nucleic of sperm and egg<br />Mammalian fertilization- Cortical Reaction hardens a zona as a block to polyspermy<br />Cortical Reaction-Lets only one sperm in and then blocks off<br />
  4. 4. C. Cleavage<br />-A period of rapid cell division without growth<br />-Result=blastomeres=large number of cells<br />-Holoblastic<br /> Complete division of egg<br />Yolk-rich eggs<br />-Meroblastic<br />Incomplete division of egg<br />Yolk-rich eggs<br />-Creates blastula, a multicellularball, which contains the blastocoel<br />
  5. 5. -Rearranges the blastula to form a three-layered embryo with a primitive gut<br />-Transforms blastula into a gastrula<br />-The gastrula contains the archenteron and three embryonic germ layers: the ectoderm, the endoderm, and the mesoderm<br />D. Gastrulation<br />
  6. 6. E. Organogenesis<br />-Organs form from the three embryonic layers<br />-Includes:<br />-Formation of the notochord by condensation of dorsal mesoderm<br />-Development of the neural tube from folding of the ectodermal neural plate<br />-Formation of the coelom from splitting of lateral mesoderm<br />
  7. 7. -Develop in a fluid-filled sac within a shell or uterus<br />-Meroblastic cleavage in the eggs of birds and reptiles is restricted to a small disc of cytoplasm at the animal pole<br />-The blastodisc forms and begins gastrulation with the formation of the primitive streak.<br />-Three germ layers give rise to the four extraembryonicmembranes:the yolk sac, amnion, chorion, and allantois.<br />-Eggs of placenta mammals=small, store little food, and exhibit holoblasticcleavage w/no obvious polarity<br />-Gastrulation and organogenesis resemble the processes in birds and reptiles<br />F. Amniote Embryos<br />
  8. 8. -After fertilization, and early cleavage in the oviduct, the blastocyst implants in the uterus<br />-Trophoblastbegins formation of fetal portion of the placenta<br />-Embryo proper develops from a single layer of cell, the epiblast, within the blastocyst.<br />-Membranes homologous to birds and reptiles function in intrauterine development<br /> F. Amniote Embryos cont.<br />
  9. 9. II. The Cellular And Molecular Basis of Morphogenesis and Differentiation In Animals<br />A. Morphogenesis<br />Cytoskeletal rearrangements are responsible for changes in both shape and position of cells<br />Involves specific changes in cell shape, position, and adhesion<br />Cell adhesion molecules on cell surfaces are also important for cell migration and for holding cells together in tissues<br />The extracellular matrix provides anchorage for cells and also helps guide migrating cells toward their destinations<br />
  10. 10. B. Fate Mapping<br />-Can reveal cell genealogies in chordate embryos<br />-Maps of embryos have shown that specific regions of the zygote or blastula develop into specific parts of older embryos <br />
  11. 11. C. Eggs of Vertebrates<br />-Have cytoplasmic determinants that help establish the body axes and differences among cells of the early embryo<br />-Cytoplasmic determinants serve as the basis for setting up differences among parts of the egg<br />-Cells that receive different cytoplasmic determinants undergo different fates<br />
  12. 12. -Drive differentiation and pattern formation in vertebrates<br />-In a developing embryo, cells interpret positional info that varies w/ location<br />-Info=form of signal molecules<br />-Special “organizer regions<br /> Dorsal lip of the blastopore<br /> Apical ectodermal ridge of the vertebrate limb bud<br />-Signal molecules influence gene expression in the cells that take them<br />Leading to differentiation and the development of particular structures<br />D. Inductive Signals<br />

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