Chapter 3 & 5 Mouse and Chick Development Flashcards
What do all amniotes have in common?
An amnion son. All amniotes can live on land because they essentially bring water with them.
What is the yolk of an egg?
It is one large cell.
Frogs develop into free swimming tadpole in 4 days. A fly is done in a day. What about a chick?
A chick takes 21 days to after laying to be done.
Early egg structure:
Chalaza,
Vitelline membrane
Blastoderm
Chalaza: is a anchor which centers the yolk in the egg
Vitelline membrane: Is a barrier which will stop other sperm from accessing the embryo, it surrounds the yolk
Gastrulation involves what in the chick embryo.
So first we have a cleavage furrow form on the germinal disk. These cleavage furrows will begin to form the blastoderm, the blastoderm will have a raised hollow area with the subgerminal space beneath it.
Subgerminal space:
the area between the blastoderm proper and the yolk beneath it.
Cells migrate accross bottom of the subgerminal space, what does this cause?
This migration forms the hypoblast.
Cells are concentrated in a circle, what is this circle called?
The area opaca surrounds the area pellucida. This is because cells are in higher concentration in the area opaca because there is no hollow zone. This hollow zone however is present in the area pellucida, making it pale and well lucid.
What is Koller’s sickle?
Koller’s sickle will appear on the posterior end of the embryo. This sickle is a thickening of cells which will extend towards the anterior region forming the primitive streak.
Koller’s sickle is of course a thickening of cells.
What will happen ultimately to the cells of the primitive streak?
These cells will migrate inwards, transitioning epithelial to mesenchymal, they will cover the hypoblast, endoblast will be induced, but most cells will become the mesoderm.
Koller’s sickle will form where?
The posterior marginal zone. in other words the posterior zone, between the borders of the area opaca and the area pellucida
Primitive streak:
Appears to be an invagination analogous to the invagination that is seen in xenopus. However they are in many ways not alike in any shape or form.
The primitive streak extends to the anterior, what happens next.
A cluster cells known as hensen’s node forms at the top. Henson’s node begins head process -> head fold -> an invagination and the neural tube formation from anterior to posterior, tracing over the primitive streak.
Henson’s node migrates down the primitive streak, from anterior to posterior, the streak zips up the nervous system behind henson’s node. Hensens node does not become the head process or head fold, the head fold/process follows it with the formation of the nervous system.
It is said that there is an anterior to posterior gradient of development in the embryo, what does this mean?
As henson’s node travel’s from anterior to posterior development travels with it. The nervous system is zipped up, the neural tube forms. The somites are outside the neural tube. Somites are mesoderm attached to stocks which will pull them out, allowing ribs and limbs to form. the outer layer’s of this flattened elongated disk will fold together, creating the body cavities. Essentially however, the key point is that development does indeed begin anterior, despite the streak beginning posterior at koller’s sickle.
Where does the notochord form in all this mess?
Yes we still form a notochord initially. It will be induced from mesoderm, underneath our neural tissue (ventral to our neural tissue) as would be seen in normal develpment for xenopus let’s say.
