1. Chapter 47
Animal Development

2. I) Stages of Early Embryonic Development
1) preformation vs. epigenesis

3. A) Fertilization
1) The acrosomal reaction a) enzymes released by acrosome b) acrosomal process penetrates the jelly coat

4. c) proteins on tip of process bind to receptors on vitelline layer, just outside of plasma membrane c1) lock and key: only sperm from that species will fit

5. d) membrane of sperm fuses with membrane of egg d1) ion channels open in egg, allowing Na into egg d2) this polarizes egg, blocking entry of any more sperm = fast block to polyspermy

6. 2) The Cortical Reaction a) egg releases Ca2+ from ER at site of sperm entry b) this spreads throughout cytosol, causing release of more Ca2+

7. c) Ca causes cortical granules to fuse with membrane and release contents into perivitelline space
d) vitelline layer separates from membrane and hardens, creating a fertilization envelope = slow block to polyspermy

8. 3) Activation of the egg a) transport of H+ out raises pH, allowing an increase in metabolism and protein synthesis a1) some protein synthesis occurs even without nucleus, so mRNA was stockpiled in egg

9. a2) activation can be artificial and without nucleus, showing that molecules involved in activation were also present in cytoplasm

10. 4) Fertilization in mammals a) similar to invertebrates b) zona pellucida surrounds the egg, which hardens after the cortical reaction to be the slow block to polyspermy

11. B) Cleavage
1) rapid division of embryo with no cellular growth between divisions a) small cells called blastomeres

12. 2) the following occurs except for mammals a) High amounts of yolk are stored in vegetal pole

13. b) animal pole has little yolk, and divides faster

14. c) in amphibians, animal pole is dark gray
c) in amphibians, animal pole is dark gray. c1) cytoplasm rotates toward point of sperm entry, leaving a grey crescent **sperm can only enter in the animal pole along the animal/vegetal border

15. 3) first two rounds of cleavage occur along animal-vegetal pole axis

16. 4) next round divides perpendicular to this, mainly in animal pole because vegetal pole is too thick. a) holoblastic cleavage: complete division of cells(sea urchin and frog)

17. b) meroblastic cleavage: b1) incomplete division from large concentration of yolk * birds: yolk is an egg cell, with small disc of yolk free cytoplasm at top of animal pole.

18. 5) Morula: solid ball of cells 6) blastula: has a fluid filled cavity called blastocoel

19. C) Gastrulation
1) production of 3 (germ) cell layers a) ectoderm: skin, hair, nervous system b) endoderm: digestive tract c) mesoderm: muscles, bones, blood

20. 2) gastrulation of sea urchin a) invagination: mesenchyme cells at vegetal pole migrate toward animal pole and pull vegetal plate up

21. b) pouch formed is called archenteron (primitive gut) c) blastopore: opening of archenteron

22. 3) gastrulation in frog a) invagination of cells forms a dorsal lip at the blastopore (at gray crescent)

23. b) cells migrate around embryo toward blastopore, until a full circle is formed, creating a yolk plug. animation

24. D) Organogenesis 1) Notochord a) dorsal mesoderm condenses
2) Neural tube
a) dorsal ectoderm folds downward and pinches off, creating a tube
video

25. 3) Somites a) clusters of mesoderm that surround the neural tube and turn into vertebrae/muscles

26. E) Amniote embryos
1) amniotic sac: fluid filled sac surrounding the embryo

27. 2) birds
a) early cleavage creates a blastodisc, a cap of cells on the yolk that create the embryo a1) epiblast a2) hypoblast a3) blastocoel

28. b) cells of upper layer roll down and into blastocoel b1) forms a primitive streak on top of blastodisc (shows anterior-posterior alignment)

29. b2) embryo only comes from epiblast

30. b3) germ layers outside of embryo become extra -embryonic membranes

31. yolk sac: nutrients. amnion: fluid filled sac around embryo
* yolk sac: nutrients * amnion: fluid filled sac around embryo * allantois: uric acid storage/ gas exchange * chorion: shock support/ gas exchange

32. 3) Mammals
a) blastocyst: circle of cells with an inner cell mass b) inner cell mass: cells that will become embryo and extra-embryonic membranes

33. c) trophoblast: outer cells that form fetal half of placenta

34. d) follows similar gastrulation as bird d1) epiblast and hypoblast form d2) yolk sac forms and creates blood cells that migrate into embryo d3) allantois turns into umbilical chord

35. II) Cellular and Molecular Basis of Differentiation
A) changes in cell shape, position, and adhesion 1) microtubules shorten or elongate to change the shape of the cell

36. 2) Convergent extension a) cells wedge in between each other, making the region narrower, but longer

37. 3) Extracellular matrix a) glycoproteins secreted by cells to control their, and other cells’, movements

38. 4) Cell Adhesion Molecules(CAMs) a) glycoproteins on the surface of a cell that bind to other CAMs

39. b) cadherins: CAM that requires Ca to function properly

40. B) Fate Mapping
1) cells and their progeny can be traced using dyes or other markers

41. C) Cytoplasmic Determinants
1) Polarity and body plan a) bilaterally symmetrical organisms have: a1) anterior-posterior axis a2) dorsal-ventral axis a3) left and right sides

42. b) established by positioning of materials in the egg

43. 2) Restriction of cellular potency a) cleavage can divide materials evenly or unevenly a1) inclusion of grey crescent allows full development

44. D) Inductive signals drive differentiation
1) The “organizer” of Spemann and Mangold a) found that the dorsal lip of blastopore controls neurulation a1) called this region the “primary organizer”