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30 Cards in this Set
- Front
- Back
Why do we study frogs/amphibians?
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- big eggs (easy to see/manipulate)
- they are easy to get/grow |
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Where does sperm bind on the frog egg? What does this cause to happen? What is now established?
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Sperm bind about 30o N of equator
This causes the cortex to rotate towards where the sperm bound, exposing gray crescent The axis of symmetry is now set up - the sperm bound on the ventral side |
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How does frog cleavage start & what is unique about it? What happens to the top vs bottom cells?
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Meridinal
Meridinal Equitorial (only in animal) Division slows down at yolk so 2nd division starts b4 1st is finished Top cells divide much more quickly so become smaller & more numberous |
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Where does the blastocoel form? (frog)
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Forms in the animal hemisphere by the expansion of the space made by the 1st cleavage
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What molecules hold the cells together? (frog)
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E-cadherins
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Where does amphibian gastrulation occur?
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At site of gray crescent
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What dictates what will become vegetal cells? (frog)
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Transcription factors VegT & Vg1 (without these, will be epidermis instead of endoderm)
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What are the three movements of cells (steps) in frog-gastrulation?
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1. invagination (bottle cells)
2. involution (prechordal plate) 3. epiboly (chordamesoderm) |
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What is bottle cell invagination? (frog)
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- migrates inward
- specialized group in this region |
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What is involution (prechordal plate)? (frog)
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- creates dorsal blastopore lip
- cells 'turn around and head in' - moves from a straight line to a curve, then to a circle (yolk plug) |
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What dives initial gastrulation in frogs?
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IMZ cells (involuting marginal zone)
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What is epiboly (chordamesoderm)?
(frog) |
- outer ectoderm
- extending outward to cover endoderm - embryo surrounded by ectoderm |
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What experiment was done to find out 'the organizer'?
(frog) |
Spemann forced a zygote to divide where the gray crescent was only on one side. The side without did not develop, so this showed that the gray crescent contained 'the organizer'.
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What happens when a dorsal blastoporal lip is transplanted elsewhere on the blastula?
(frog) |
TWO gastrulations occur!
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What happens if the animal region is put directly on top of the vegetal region?
(frog) |
The animal region will become the mesoderm!
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What tells the organizer to become the organizer?
What is this composed of? (frog) |
The Nieuwkoop center
This is where the mesoderm signal (from underlying endoderm) and the dorsal signal (B catenin from gray region) overlap |
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What are the details of the 'dorsal signal'?
(frog) |
B-catenin is expressed everywhere
But Disheveled only expressed in area that moves to side when cortex rotates.... Wnk activates Frizzled activates Dishevled INHIBITS GSK-3 from breaking down B-catenin So B-catenin is high conc in this region - this is the DORSAL SIGNAL |
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What are the functions of the organizer?
(frog) |
1. Self-differentiate dorsal mesoderm (prechordal plate, chordamesoderm)
2. Dorsalize surrounding mesoderm 3. Dorsalize ectoderm (neural tube) 4. Initiate gastrulation movements |
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What type of cleavage is frog cleavage?
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displaced radial mesolecithal holoblastic
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What type of cleavage is bird cleavage?
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discoidal telolecithal meroblastic
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What is the name of the layer on the yolk that becomes the embryo? (bird)
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Blastodisk/blastoderm
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How does the blastoderm form? (bird)
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A layer of cells on top of yolk divide & become 5-6 layers thick
Then all but the top layers & some on the edges die off, leaving 1 cell layer thick 1 cell layer thick - area pellucida More cells on edges - area opaca |
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What is the precise layer of cells in the blastoderm that will become the embryo? (bird)
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Epiblast
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What are the 2 migrations that form the hypoblast? (bird)
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1. Delamination
2. Epithelial sheet from posterior margin |
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What happens in delamination? (bird)
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Epiblast cells delaminate & move to form a 2nd layer between epiblast & yolk as hypoblast islands
Cells from the posterior margin migrate forward and link the islands Forms the hypoblast |
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What is the area between hypoblast and epiblast? (bird)
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Blastocoel
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What happens during secondary hypoblast formation? (bird)
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Cells originating from Koller's sickle in the posterior margin move forward & push the primary hypoblast cells forward
As the 2nd cells move forward, signal the epiderm above them to thicken & differentiate (& narrow - convergent extention) & form PRIMATIVE STREAK |
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Where does the primitive groove form & what else forms there, and what does the essentially act like? (bird)
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Primitive groove forms at anterior end with primitive pit
Primitive groove acts like blastopore |
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What is the order of ingression through Henson's node? (bird)
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1st - head in, pharyngeal endoderm
2nd - head in & up, head mesenchyme & prechordal plate 3rd - head in, chordamesoderm |
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What happens as the cells move inwards? (bird)
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pushes out hypoblast
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