1x haploid Fertilized zygote Pronuclei n2 1 Fert hours after

1x haploid fertilized zygote pronuclei n2 1 fert

  • Notes
  • dannybrown
  • 51
  • 100% (1) 1 out of 1 people found this document helpful

This preview shows page 11 - 26 out of 51 pages.

1x (haploid)
Image of page 11
Fertilized zygote Pronuclei (n=2) 1. Fertilization: 12-24 hours after ovulation 2. One-cell stage: two pronuclei fuse (zygote) 3. First cleavage : two-cell stage 30 hours post ovulation
Image of page 12
2 cell stage During the 1st week, cells continue to undergo cleavage* Cells become smaller, form into a ball - morula (12-32 cells) - blastula (128 cells), around a central cavity - blastocyst (700-800 cells) morula blastula 4 cell stage blastocyst *using up energy reserves!
Image of page 13
inner cell mass --> embryoblast (future organism) outer cell mass --> trophoblast (supporting structures)* Cells in blastocyst have already begun to change (differentiate) *more on the trophoblast next week
Image of page 14
Blastocyst implants into uterine wall ( 50% chance...) WEEK TWO The embryoblast divides into two layers: Epiblast (top): future embryo Hypoblast (below): yolk sac
Image of page 15
From here on, we will focus on just the embryo How do we go from a bunch of cells, the epiblast, to forming all the structures and tissues of the embryo?
Image of page 16
GASTRULATION! (Gastrula is Latin for ² stomach ³ )
Image of page 17
Gastrulation is the formation of the three germ layers (cell lineages) common to all animals A process of migration and differentiation -Creates an embryo with three layers : ectoderm mesoderm endoderm -Creates a gut tube ( endoderm ) -Creates a central rod ( notochord )
Image of page 18
Gastrulation in amphibians:
Image of page 19
caudal (tail) cephalic (head) If you were to view gastrulation from the top (in mammals), you ± d see the primitive streak grow from the caudal (tail) end toward the middle
Image of page 20
Cells in midline of epiblast dive down & spread out As they migrate, they form two new layers: mesoderm endoderm The epiblast layer becomes ectoderm Side view Top view
Image of page 21
Notochord (stiffened rod of mesoderm; future ² core ³ of axial skeleton) IN ALL VERTEBRATES (actually chordates), another important event happens during gastrulation:
Image of page 22
Here ± s what the embryo looks like in a section after gastrulation:
Image of page 23
A movie of gastrulation (courtesy Univ. of Montréal):
Image of page 24
(Cranial end of embryo) SO, what is the embryo like after three weeks?
Image of page 25
Image of page 26

You've reached the end of your free preview.

Want to read all 51 pages?

  • Fall '10
  • AndrewA.Biewener,PeterT.Ellison,andDanielE.Lieberman
  • Developmental Biology, Neural tube, Mesoderm

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes