Mammals

Question 1

Why is it difficult to study development in mammals?

Answer 1

Completely internal

Question 2

Where does fertilization occur?

Answer 2

Oviduct

Question 3

Where do the early stages of development occur?

Answer 3

Fallopian tubes

Question 4

What type of yolk distribution is seen in mammals?

Answer 4

Isolecithal

Question 5

What type of cleavage is seen in mammals?

Answer 5

Holoblastic, rotational

Question 6

How does a morula become a blastocyst?

Answer 6

Compaction of cells

Question 7

How does compaction occur to form a blastocyst?

Answer 7

Changes in cell adhesion through E-caderins, which increase the contact area between cells and causes really tight packing, and from cytoskeletal rearrangements

Question 8

What are the two cell types in a blastocyst?

Answer 8

Trophoblast and ICM

Question 9

At what cell stage do the trophoblast and ICM become specified?

Answer 9

32 cells

Question 10

What are the 2 transcription factors that specify if a cell will become part of the trophoblast or part of the ICM?

Answer 10

Oct4 and Cdx2

Question 11

What does the trophoblast become?

Answer 11

Extra-embryonic tissue. It becomes the chorion

Question 12

What does the ICM become?

Answer 12

The embryo and the amnion

Question 13

Which transcription factor specifies trophoblast?

Answer 13

Cdx2

Question 14

Which transcription factor specifies ICM?

Answer 14

Oct4

Question 15

What does Cdx2 do?

Answer 15

Inhibits Oct4 to specify cells to become trophoblast cells

Question 16

What does Oct4 do?

Answer 16

Inhibits Cdx2 and turns on Sox2 to specify ICM cells

Question 17

What does Sox2 do?

Answer 17

Promotes its own activity and the activity of Oct4. Turns on Nanog transcription

Question 18

What does Nanog do?

Answer 18

Promotes activity of Oct4, Sox2 and itself

Question 19

How does implantation of the blastocyst in the uterus occur?

Answer 19

Cell adhesion. First through labile interactions then through permanent interactions

Question 20

What creates the labile interactions that lead to implantation?

Answer 20

Sulfated polysaccharides on the endometrium bind to L-secretin on the blastocyst

Question 21

What creates the permanent interactions that lead to implantation?

Answer 21

P-cadherin is expressed by both the blastocyst and the endometrium

Question 22

What cell movement splits the ICM into 2 layers?

Answer 22

Delamination

Question 23

What are the 2 layers formed when the ICM splits into 2 layers? What do they become?

Answer 23

Hypoblast forms the yolk sac and epiblast forms the amnion and embryo

Question 24

In mammals, the positioning of the germ layers and the cell movements are very similar to which animal?

Answer 24

Chickens

Question 25

Which germ layer ends up in the original place of the hypoblast?

Answer 25

Endoderm

Question 26

Which germ layer ends up in the original place of the epiblast?

Answer 26

Ectoderm

Question 27

What are the 2 cell layers that make up the placenta?

Answer 27

Cytotrophoblast and syncytiotrophoblast

Question 28

What is the cytotrophoblast?

Answer 28

A single layer of cells around the embryo

Question 29

What is the syncytiotrophoblast?

Answer 29

A large network of cytoplasm that forms extracellular spaces in the growing tissue

Question 30

How is the umbilical chord formed?

Answer 30

Differentiation of fetal blood vessels that connect with the mother's vessels in the placenta

Question 31

What are the 3 types of twins?

Answer 31

Monozygotic, dizygotic, conjoined

Question 32

How genetically similar are identical twins?

Answer 32

Identical genetic makeup

Question 33

How many amnions and chorions would be created for a set of monozygotic twins that had the zygote split very early on?

Answer 33

2 amnions and 2 chorions. Early splits form two blastocysts that both implant and each one has tissues specified into trophoblast and ICM

Question 34

How many amnions and chorions would be created for a set of monozygotic twins that had the ICM split?

Answer 34

Two amnions and 1 chorion. The trophoblast and ICM are already specified, so each embryo still has its own amnion but they share trophoblast tissue

Question 35

How many amnions and chorions would be created for a set of monozygotic twins that had the zygote split very late?

Answer 35

1 amnion and 1 chorion. The embryo would have split after some of the ICM branched off into the amnion, so the embryos share an amnion

Question 36

How do dizygotic twins occur? How genetically similar are they?

Answer 36

Two eggs get ovulated and they both get fertilized and implanted. They are no more similar to each other than regular siblings

Question 37

What are conjoined twins?

Answer 37

Twins that share some organs and tissues

Question 38

What are 3 possible causes for conjoined twins?

Answer 38

1. A second organizer is created and creates a new body axis 2. Trauma that splits the epiblast 3. Confused Nodal