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Do Now Identify each of the cells in the diagram and indicate the

Do Now Identify each of the cells in the diagram and indicate the Human chromosome number of each. Sperm (23). Egg (23). Zygote (46). How do we go from a zygote (a single cell) to a multicellular organism? (hint: think about a process used to increase cell#).

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Do Now Identify each of the cells in the diagram and indicate the

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  1. Do Now Identify each of the cells in the diagram and indicate the Human chromosome number of each. Sperm (23) Egg (23) Zygote (46)

  2. How do we go from a zygote (a single cell) to a multicellular organism? (hint: think about a process used to increase cell#)

  3. STAGES OF EMBRYONIC DEVELOPMENT • Series of steps leading from zygote to organism • Cleavage– increase in cell# by rapid mitosis, no cell growth 2. Differentiation – cells get their jobs by “reading” different parts of DNA, form tissues and organs 3. Growth

  4. Stage 1 • Egg and sperm are produced by MEIOSIS (gametogenesis). • They contain half as much genetic material as parent cells (in humans = 23) • The joining of the two nuclei is called fertilization • This can occur internally or externally

  5. Stage 2 1 • The fertilized egg or Zygote now has how many chromosomes? The spermapproachesthe egg 2 The sperm’senzymesdigest the egg’s jelly coat SPERM 3 The plasma membranesof sperm and egg fuse Spermhead The spermnucleus enters the egg cytoplasm 4 46 Nucleus • Normal fertilization: http://www.stanford.edu/group/Urchin/nfert.htm Spermnucleus Eggnucleus Jellycoat The nucleiof spermand egg fuse 5 EGG CELL Zygotenucleus

  6. Stage 3 2-cell stage • The fertilized egg divides into two new cells by MITOSIS to form identical cells • This is the beginning of cleavage: rapid increase in cell #’s by mitosis (stages 3-4) • NO CELL GROWTH! • # of chromosomes in each cell:46 http://fig.cox.miami.edu/~cmallery/150/devel/blastula.gif

  7. Stage 4 • Four Cell Stage: still increasing in numbers by mitosis (cleavage) • Number of chromosomes in each cell: 46

  8. Stage 5 • Blastula: hollow ball stage • Number of chromosomes in each cell: 46 • The layer of cells is generally one cell thick and the cavity is filled with fluid • Cell growth starts

  9. Stage 6 • Gastrulation: inward pushing of blastula to form two layers (indentation) • The cell is beginning to grow before dividing

  10. Stage 7 • Differentiation: formation of three layers which will develop into organs and organ systems • Development can take place internally or externally

  11. Twins • Fraternal Twins – two separate eggs fertilized by two separate sperm (dizygotic) • Identical Twins – single egg is fertilized , zygote splits early (monzygotic), have identical DNA

  12. Indian girl - born fused at the pelvis to a "parasitic twin" that stopped developing in the womb • She had absorbed the organs and body parts of the other fetus, a condition that occurs once in 50,000 conjoined twin births.

  13. Fertilization and Cleavage Video Clip • http://trc.ucdavis.edu/biosci10v/bis10v/media/ch27/cleavage_implant.html • http://www.unc.edu/~fconlon/DanielResearch.htm • http://raven.zoology.washington.edu/celldynamics/events/workshops/archive/2003/cytomod_abstracts/GvD_VDF/images/GvD-VEF-fig1.jpg • http://www.howstuffworks.com/adam-200048.htm

  14. Stem cells – cells without a “job”, removed from blastocyst before they differentiate

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