Chickens

Question 1

Why is the amniotic egg an important adaptation to the terrestrial environment?

Answer 1

Eggs were no longer tied to water

Question 2

What are the 4 extra-embryonic membranes in amniotes?

Answer 2

Chorion, yolk sac, amnion and allantois

Question 3

What is the function of the amnion?

Answer 3

Surrounds the embryo and provides an aqueous environment

Question 4

What is the function of the chorion?

Answer 4

Surrounds everything and allows gas exchange. Keeps the inside of the egg sterile

Question 5

What is the function of yolk sac?

Answer 5

Nutrition

Question 6

What is the function of allantois?

Answer 6

Holds metabolic waste products

Question 7

How does the egg get formed in a chicken?

Answer 7

Chickens have only 1 ovary, and ovulation happens from there. The egg gets fertilized and the albumen is added. Then the egg passes the shell gland and get rotated as it is covered with a calcified shell. The egg is laid out of the cloaca

Question 8

What type of yolk distribution do chickens have?

Answer 8

Telolecithal

Question 9

What type of cleavage do chickens have?

Answer 9

Meroblastic, discoidal

Question 10

What are the two zones of the blastodisc?

Answer 10

Area opaca and area pellucida

Question 11

What is the subgerminal cavity?

Answer 11

The cavity between the animal cells in the blastodisc and yolk

Question 12

How is the primary hypoblast created?

Answer 12

Delamination from the epiblast to create hypoblast islands, which then expand

Question 13

What does the primary and secondary hypoblast become in chicken embryos?

Answer 13

Nothing, they act as scaffolding

Question 14

Where does the secondary hypoblast come from? What does it do?

Answer 14

Comes from the posterior marginal zone. It pushes the primary hypoblast out of the way and causes expansion of the primitive streak

Question 15

What does Koller’s sickle do?

Answer 15

Directs cell movements

Question 16

What is the primitive streak? How it is formed?

Answer 16

A darkened line on the dorsal side of the embryo that is the site of gastrulation. Created by delamination and intercalation of epiblast cells along the midline

Question 17

What causes the elongation of the primitive streak?

Answer 17

Movement of the secondary hypoblast beneath it and convergent extension of the posterior epiblast cells

Question 18

Where does gastrulation occur?

Answer 18

Front end of the primitive groove

Question 19

What is the organizer in the chicken embryo? Where is it? What does it become?

Answer 19

Hensen’s node, located at the anterior end of the primitive groove. Becomes the notochord

Question 20

Why does gastrulation occur through epithelial-mesenchyme transitions?

Answer 20

There is too much yolk for the cells to move around freely, so they need to become mesenchymal cells to be able to move

Question 21

What is the fate of the cells that go through the primitive groove first? Where along the primitive streak do those cells go through?

Answer 21

The first cells are future endoderm. They go through at the posterior end, far away from Hensen’s node

Question 22

What is the fate of the cells that go through the primitive groove second? Where along the primitive streak do those cells go through?

Answer 22

Future mesoderm cells. They go through between Hensen’s node and the posterior end, but aren’t particularly close to Hensen’s node

Question 23

Where are the future ectoderm cells found relative to the primitive streak?

Answer 23

They stay on the dorsal side and don’t go through the primitive groove. The cells surrounding Hensen’s node become neural ectoderm and the ones further away become epidermal ectoderm

Question 24

What is happening to the primitive streak during gastrulation?

Answer 24

It is regressing back towards the posterior end

Question 25

What is happening at the same rate as the regression of the primitive streak?

Answer 25

Elongation of the notochord

Question 26

What are the ectoderm cells doing while the primitive streak is regressing?

Answer 26

Expanding over the yolk through epiboly through the use of fibronectins signals

Question 27

What structures are homologous to Hensen’s node in frogs and fish?

Answer 27

The dorsal blastopore lip in frogs and the embryonic shield in fish

Question 28

What two signals are the marginal cells in the posterior marginal zone expressing?

Answer 28

Wnt8c and Vg1

Question 29

What type of signal is Wnt8c? What does it do?

Answer 29

Paracrine factor in the Wnt pathway. It allows beta-catenin activity

Question 30

What signal gets expressed when both Vg1 and Wnt8c are expressed? Where is it expressed?

Answer 30

Nodal. Gets expressed in epiblast near Koller’s sickle

Question 31

What transcription factor is expressed in primary hypoblast cells?

Answer 31

Cerberus

Question 32

What does Cerberus do?

Answer 32

Inhibits Nodal

Question 33

How does Nodal expression expand towards the anterior end when Cerberus is inhibiting it?

Answer 33

When the secondary hypoblast expands, it pushes away the primary hypoblast that is expressing Cerberus and Nodal is no longer inhibited

Question 34

Why is the expansion of Nodal expressing cells and the regression of Cerberus expressing cells so critical?

Answer 34

Makes sure the organizer is in the right place

Question 35

What are 6 signals expressed by Hensen’s node?

Answer 35

Goosecoid, chordin, noggin, nodal, BMP antagonists and FGF

Question 36

What does Goosecoid do?

Answer 36

A transcription factor that shuts off non-brain genes

Question 37

Where is Smad1 expressed?

Answer 37

Epidermal ectoderm

Question 38

How does FGF help specify the neural plate cells? (4 things)

Answer 38

It promotes Nodal activity and makes cells less sensitive to BMP signalling molecules. It regulates the transcription of ectoderm cells to stop them ingressing through the primitive streak and produce molecules that are involved in neural tissue production