Asymmetric meiosis

Fertilization in ampulla, takes 24 hrs to complete 1st cleavage, 1 division per day, hatch at 5-7 days; Ectopic pregnancies

Before and after compaction between 8-16 cell stage; at 8 cell stage all blastomeres = (totipotent; become whole animal); after compaction outer and inner cells with different fates (inner cell mass or trophectomderm; loss of potency; commitment to different lineage; if take outer cells and place inside still become te; overt differentiation

Fate – what you will become if left in place – fate map; potent – capacity to change direction

Where and when

Inner cell mass + te + blastocoel. Always touch down to uterine lining at embryonic pole

Note again separation of lineages

lineages

First sign of gastrulation; formation of primitive streak at posterior/caudal/tail end of animal. Our gastrulation is more like chick; as if epiblast is floating on top of yolk mass; mouse gastrulation makes special accomodations for small space and may or may not be an exact model of humans.

Fate map. Epiblasts who will migrate are already committed.

Role of hypoblast in directionality of primitive streat

Epithelial to mesenchymal transition

Epiblast are progenitor cells. From whence they enter the ps or pn and when will play a significant role in determining their fate. Discuss routes for axial, paraxial, heart, intermediate and lateral plate (except for heart.

At end of gastrulation movements axial, heart primordium, from paraxial to lateral plate a loosely connection stream of mesenchymal cells; retreat of primitive streak/node.