Biology 202 - Lecture 1

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Biology 202 - Lecture 1
2011-03-06 17:58:15

Vertebrate Origins and Basic Design
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  1. Course Framework: The Craniata
    • No vertebrates are more or less 'highly evolved' or 'advanced'!
    • some are more complex than others
    • humans are actually fancy fish!
  2. R e l a t i o n s h i p s
  3. Where do vertebrates fit in the animal kingdom?
    • probably originated in the early Cambrian, ~550 mya
    • probably originated by paedomorphosis (sexual maturation ofthe larval form) of a urochordate-like ancestor
    • underwent a duplication of the Hox genes, which controldevelopment, at the time of their origin
  4. Vertebrates possess all the defining characteristics of the taxa towhich they belong...
    • euchordata: noto chord persists in adult ,myotomes, caudal fin
    • Chordata: notochord in embryo, post anal tail, dorsal nerve tube
    • deuterostomata: pharyngeal slits
    • coelomata: body cavity
    • bilateria: bilateral symmetry, 3 germ layers, motile
    • Metazoa: multicellular, heterotrophic, gonads, collagen
    • BUT, these do not define vertebrates
  5. What are the defining characteristics of vertebrates?
    • Embryonic development is unique, and includes four main steps
    • I. Cleavage
    • II. Gastrulation
    • III. Neurulation
    • IV. Organogenesis
    • Vertebrate organ systems also have many unique characteristics
  6. I. Cleavage
    • The zygote divides to form ablastula (a fluid-filled ball of cells).
    • Cells remain unspecialized.
  7. II. Gastrulation
    • Cells of the blastula move inward at the blastopore to form agastrula, a hollow ball with three cell layers:
    • endoderm (which will form the gut lining
    • ectoderm(epidermis, nervous system)
    • mesoderm(everything else)
  8. III. Neurulation
    • Dorsal mesoderm cells aggregate to form the notochord - a supporting rod
    • - Following induction by the notochord, dorsal ectoderm folds into a dorsal hollownerve cord and neural crest cells
    • Mesoderm flanking the notochord becomes segmented intosomites, which will form segmental structures.
    • Pharyngeal pouches form along the pharynx.
    • Ectodermal placodes form at the eye, ear & nostrils
    • The pharyngula is very similar among all vertebrates
  9. IV. Organogenesis
    • Embryonic cells specialize, forming tissues, organs andorgan systems
    • differential cell growth and death results in different bodyshapes