1. pre-embryonic phase
    • weeks 0-2
    • fertilization up to gastrulation
  2. embryonic stages
    • weeks 3-8
    • gastrulation to basic body plan
    • establishment of major body axis, organs, external form
  3. fetal development phase
    • weeks 9 - birth
    • further growth and organ and tissue maturation/development
  4. blastocyst
    • day 4.5 - 6
    • includes: inner cell mass,¬†blastocyst cavity,¬†outer cell mass (trophoblast)
    • implants into uterine wall
  5. inner cell mass
    precursor to all tissues in body
  6. blastocyst cavity
    fluid filled
  7. outer cell mass / trophoblast
    precursor to supporting membranes of placenta
  8. sequence of key events in early development
    gametogenesis, fertilization, cleavage, blastocyst formation, implantation, gastrulation and neurulation, neural crest formation
  9. gastrulation
    • sweeping cellular movements which generate 3 key cell layers
    • ectoderm, mesoderm, endoderm
  10. ectoderm
    key structures
    • outer covering of the body (skin, hair, sweat glands, etc)
    • nervous system (from neural tube)
    • neural crest (considered it's own layer)
  11. endoderm
    key structures
    inner organs and their lining (gut tube and organs from it, pharyngeal pouches, lunchs and trachea, bladder)
  12. mesoderm
    key structures
    • middle (muscles, blood vessels, heart, skeleton, kidneys, spleen, sex organs)
    • paraxial (nearest to dorsal midline), intermediate, lateral
  13. neural crest
    key structures
    • neurons, cartilage and bones in head, dentine of teeth, melanocytes (pigment in skin and hair)
    • derived from ectoderm
  14. What are the ways by which cells with the same genes controlled to express different genes?
    • internal determinants
    • external signals
  15. internal determinants
    role in differential gene expression
    • internal determinans are asymmetrically located in precursor cell and thus are unevenly distributed in daughter cells
    • ie frog eggs with pigment and yolk and location of specific mRNA molecules
  16. exteral signals
    role in differential gene expression
    • external signals coming from cells themselves can control the fates of cells around them
    • ie eye lens formation
Card Set
lecture 1