Week 2

Question 1

What occurs during the cleavage stage?

Answer 1

A series of mitotic divisions transform egg cytoplasm into many small nucleated cells called blastomeres.

Question 2

What is unique about cleavage divisions?

Answer 2

Cleavage divisions have a unique cell cycle and result in a progressive reduction of cytoplasmic volume.

Question 3

What controls the rates of cell division and blastomere distribution during cleavage?

Answer 3

They are generally under the control of mRNAs and proteins stored in the oocyte.

Question 4

How rapid is cleavage in most species?

Answer 4

In most species, cleavage is very rapid.

Question 5

How does the cell cycle differ in early embryos compared to somatic cells?

Answer 5

Early embryos lack G1 and G2 phases and are biphasic, only having S and M stages.

Question 6

What role do microtubules play during cleavage?

Answer 6

Microtubules (tubulin) separate chromosomes.

Question 7

What is the function of actin filaments during cleavage?

Answer 7

Actin filaments make up the contractile ring used to separate cells.

Question 8

What is karyokinesis?

Answer 8

Karyokinesis (Mitosis) is the division of the nucleus (naryon).

Question 9

How does the positioning of the mitotic spindle affect daughter blastomeres?

Answer 9

The positioning of the mitotic spindle determines the position of the two daughter blastomeres.

Question 10

What is the relationship between the mitotic spindle and the contractile ring?

Answer 10

The mitotic spindle and contractile ring are always perpendicular; the orientation of the mitotic spindle determines the plane of cytokinesis.

Question 11

How is cytoplasm proportioned between daughter cells?

Answer 11

Cytoplasm may be proportioned evenly or unevenly between daughter cells, depending on the position of the contractile ring.

Question 12

What are the two types of cleavage patterns?

Answer 12

Cleavage patterns can be holoblastic or meroblastic.

Question 13

What factors affect cleavage patterns?

Answer 13

Cleavage patterns are further classified depending on how yolk disposition affects the cleavage pattern.

Question 14

What does the distribution of yolk determine?

Answer 14

It determines where cleavage can occur and the relative size of blastomeres.

Question 15

What are the terms for egg poles with different yolk concentrations?

Answer 15

The egg pole with rich yolk is termed the vegetal pole, while the region with low yolk concentration is termed the animal pole.

Question 16

What specific factors in egg cytoplasm influence cleavage?

Answer 16

They can influence the position and angle of the mitotic spindle and the timing of its formation.

Question 17

What is asymmetric cell division?

Answer 17

Asymmetric cell division sets up differences between cells, as seen in the first division in C. elegans, which gives two unequal daughter cells, AB and P1.

Question 18

What triggers the establishment of PAR polarity domains in C. elegans?

Answer 18

The establishment of PAR polarity domains is triggered by paternal centrosomes which contract the cell cortex.

Question 19

What happens after cleavage?

Answer 19

After the end of cleavage, you get a ball of cells called a blastula, which is hollow in the middle with liquid.

Question 20

How is the blastula formed?

Answer 20

It results from pumping ions into this space and the movement of water into it via osmotic processes.

Question 21

What are triploblasts?

Answer 21

Organisms with three germ layers: ectoderm, mesoderm, and endoderm.

Question 22

What establishes the basic body plan in development?

Answer 22

Conserved mechanisms that set up axes early in development.

Question 23

What are the three germ layers?

Answer 23

Ectoderm (outer layer), mesoderm (middle layer), endoderm (inner layer).

Question 24

What is the first sign of invagination during gastrulation in sea urchins?

Answer 24

A central inbending of cells at the center of the vegetal plate.

Question 25

What is the starting point of gastrulation in sea urchins?

Answer 25

Bastula.

Question 26

What characterizes the animal pole in sea urchins?

Answer 26

More rapidly dividing, less yolky cells.

Question 27

What characterizes the vegetal pole in sea urchins?

Answer 27

Slower dividing, more yolky cells.

Question 28

When is the AV axis set up in sea urchins?

Answer 28

Before fertilization.

Question 29

What processes underlie gastrulation?

Answer 29

Cell movement and changes in cell shape.

Question 30

What causes changes in cell shape during gastrulation?

Answer 30

Altering the cytoskeleton.

Question 31

What role does actin play in gastrulation?

Answer 31

It can create a contractile network leading to apical constriction.

Question 32

What is apical constriction?

Answer 32

Bundles of contractile filaments composed of actin and myosin contract at the outer edge of a small number of adjacent cells, creating a wedge shape.

Question 33

What are cell adhesion molecules (CAMs)?

Answer 33

Proteins that facilitate differential cell adhesion, crucial for development.

Question 34

What types of proteins are included in CAMs?

Answer 34

Cadherins, immunoglobulin superfamily proteins, and integrins.

Question 35

How do changing patterns of CAMs affect cell arrangement?

Answer 35

They force cells into new arrangements.

Question 36

What is the binding characteristic of cadherins?

Answer 36

They generally bind homophilically.

Question 37

What are the effects of gastrulation?

Answer 37

Establishes three main layers (endoderm, mesoderm, ectoderm), sets up body plan for the future embryo, and allows for cell proliferation, differentiation, and morphogenesis.

Question 38

What is key during gastrulation?

Answer 38

Cell specification.