Class Notes (807,465)
Canada (492,646)
Biology (6,677)

8-Chick Gastrulation.pdf

12 Pages
Unlock Document

Western University
Biology 3338A
Sashko Damjanovski

-  Chicks are amniotes -  Have amniotic sac, form extra embryonic tissues like we do -  Don’t attach to uterus, don’t really have placenta in same way -  Have huge yolk, embryo forms in sac on top of yolk, uses yolk to feed off of -  Extra embryonic tissues to latch onto yolk and use it, attach to nutrient source -  Big egg, won’t cleave egg -  Undergo discoidal meroblastic cleavage -  Cell movement on top of yolk -  Embryo forms something called blastodisc -  Initially: one fertinlized 2n nucleus in yolk, nucleus starts to form membranes, end up with cellular yolk-free group of cells called blastodisc sitting on top of yolk -  Initially 1 cell layer thick, doesn’t contain yolk, forming cells on top of yolk -  Cleavages not going through yolk, form clear area called blastodisc 1 -  Surface of yolk -  End up with fertilized 2n nucleus, will divide and start to form cells on top, don’t cleave into yolk, are free of yolk basically -  Cleavages on top of yolk, initially 1 cell layer thick (blastodisc), eventually thicker -  Get layer of cells sitting “on top” of yolk -  Cells then begin to secrete albumin beneath them -  Taking proteins from above, secretiing below, form cavity beneath them (underneath blastodisc) = subgerminal cavity -  Once it is formed, most cells in blastodisc undergo apoptosis and die -  Need cells to get action, then lots undergo apoptosis -  Looking down on blastodisc – bottom pic, now lots of cells have died -  In middle: only 1 cell layer thick! -  Looking through 1 cell layer, can see through it and into subgerminal cavity -  Around margins of subgerminal cavity: several cell layers, several cells around margins, more than 1 cell layer thick = marginal zone, several cell layers thick 2 More what blastodisc looks like Cells on yolk,around outside = thicker, marginal zone – area opaca, middle = area pellucida, clear Cells on yolk, divides, forms sheet of cells, pump albumin below, form sub caivty, cells die, then area pellucida, epiblast will form proper embryo Posterior marginal zone will be posterior As gastrulation occurs, anterior will be opposite, things grow posterior to anterior 3 Oct. 28 Cell rearrangements Chickens (amniotes) similar to humans, epiblast, primitive streak Our gastrulation more complicated, reason they’re complicated = extra embryonic tissues, needed for nutrients but not part of embryo proper Happening in huge egg w/ huge yolk Meroblastic discoidal cleavages In structure called blastodisc/epiblast Group of cels on top of yolk, multiply, form cavity underneath them (subdermal cavity), lots of those cells die, left with zona pelllucida (single layer of cells called epiblast) Some cells will come from area pellucida, some from PMZ, form hypoblast Will make blastocoel cavity Koller’s sickle: part of PMZ, sometimes synonymous with PMZ 4 Sitting on top of yolk, subgerminal space, blastodisc (derm), destroyed most of cells, most = epiblast forms embyro Marginal zone should be area opaca, goes around margins Area pellucida = area under epiblast Posterior marginal zone – thicker area on one side Should be more cells under anterior side Next thing: need to form blastocoel cavity Subgerminal space = NOT blastocoel Form from cells coming from epiblast and from posterior marginal zone Will get 2 types of cell movements 1.  Delaminate from epiblast – means cells going from 1 layer onto other layer, cells come down and form other layer 2.  Migrating out from posterior marginal zone Form layer of cells called hypoblast 5 Forming primitive streak Epiblast patterned by this, looking down on yolk in diagram, on top of yolk = embryo, lots of cells, in middle = area pellucida (epiblast) marginal zone w/ more cells around outside, thicker part = posterior marginal zone Rotate: just looking at epiblast layer, still sitting on top of yolk Some epiblast cells are special, mat dets that other cells don’t have Some cells have cell surface sugar called HNK1, found in other cell types, not specific to this Function has nothing to do with these cells Cells that will form primitive streak have HNK1, some cells have HNK1, like micromeres have Bcat
More Less

Related notes for Biology 3338A

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.