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

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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