Cleavage.

Question 1

Cleavage is characterised by what?

Answer 1

Rapid cell divisions.

Question 2

When does transcription in the cleavage stage occur?

Answer 2

About 1/2 way through.

Question 3

What drives transcription in the early stages of transcription?

Answer 3

Maternal mRNAs.

Question 4

What are the 5 types of holoblastic cleavage?

Answer 4

Radial.

Unequal.

Spiral.

Bilateral.

Rotational.

Question 5

Cleavage patterns are usually determined by what?

Answer 5

The amount of yolk in the egg.

Question 6

What controls the timing of the cleavages and the mitotic spindles?

Answer 6

The genes of the organism.

Question 7

What kind of eggs have holoblastic cleavage?

Answer 7

Isolecithal and mesolecithal eggs have holoblastic cleavage.

Question 8

What does holoblastic cleavage look like?

Answer 8

The cleavage plane will penetrate through the entire egg.

Question 9

What type of eggs have mesoblastic cleavage?

Answer 9

Telolecithal and centrolecithal eggs have mesoblastic cleavage.

Question 10

What does mesoblastic cleavage look like?

Answer 10

The cleavage planes do not penetrate through the yolk.

Question 11

What is a morula?

Answer 11

Once there are 16-64 cells making up the embryo, we call it a morula.

Question 12

How many cells are needed to make a blastula?

Answer 12

More than 128.

Question 13

What are the 2 types of mesoblastic cleavage?

Answer 13

Discoidal.

Superficial.

Question 14

Radial holoblastic cleavage results in cells that are all what size?

Answer 14

All the same size.

Question 15

The type of organisms that have radial holoblastic cleavage will have what kind of symmetry?

Answer 15

Radial symmetry.

Question 16

What organism does radial holoblastic cleavage take place in?

Answer 16

The sea cucumber.

Question 17

What kind of cleavage do sea urchins undergo?

Answer 17

Sea urchins undergo unequal holoblastic cleavage.

Question 18

Are the blastulas created by unequal holoblastic cleavage always equal in size?

Answer 18

The divisions of the blastomeres are not always symmetrical and can differ in size.

Question 19

What cells are formed on the vegetal half of a blastomere formed by unequal holoblastic cleavage?

Answer 19

4 macromeres which are large cells and 4 micromeres which are very small.

Question 20

What cells are formed on the animal half of a blastomere formed by unequal holoblastic cleavage?

Answer 20

8 mesomeres.

Question 21

What do the mesomere cells form?

Answer 21

The ectoderm.

Question 22

What kind of cleavage occurs in amphibians?

Answer 22

Unequal radial holoblastic cleavage.

Question 23

What happens with the cleavage events in unequal radial holoblastic cleavage.

Answer 23

the cleavage events do not wait for the previous cleavage event to finish.

This is because, when the cleavage furrow hits the dense yolk, it has to slow down.

Question 24

How do the animal and vegetal hemisphere differ after unequal radial holoblastic cleavage?

Answer 24

In the animal hemisphere there are many rapid divisions which produce many, very small blastomeres.

In the vegetal half the divisions are much slower and create fewer, large blastomeres.

Question 25

What kind of cleavage occurs in snails and molluscs?

Answer 25

Spiral holoblastic cleavage.

Question 26

What causes the tilt in the cleavage furrows in spiral holoblastic cleavage?

Answer 26

There is a change in the orientation of the spindle which causes a tilt in the cleavage furrows.

Question 27

How does the tilt occur?

Answer 27

At the 8 cell stage there is spindle that forms at the animal end of the cell and this spindle is at an oblique angle. This causes the smaller cells to fit into the cleavage furrow of the larger cells underneath.

Question 28

The direction of the cleavage tilt is determined by what?

Answer 28

The genotype of the mother.

Question 29

In spiral holoblastic cleavage does a blastocoel form?

Answer 29

No.

Question 30

Bilateral holoblastic cleavage occurs in which organism?

Answer 30

Tunicates.

Question 31

In an embryo caused by bilateral holoblastic cleavage, how many planes of symmetry are present?

Answer 31

1.

Question 32

Rotational holoblastic cleavage occurs in which organisms?

Answer 32

Mammals.

Question 33

How does rotational holoblastic cleavage occur?

Answer 33

Blastomeres divide in different ways. The 1st cleavage is meridional. The 2nd is meridional in 1 blastomere and equatorial in the other.

Question 34

What is the outer layer of a blastocyst called?

Answer 34

The trophoblast.

Question 35

What is the inner layer of a blastocyst called?

Answer 35

The inner cell mass.

Question 36

How many cells form the morula in rotational holoblastic cleavage?

Answer 36

16.

Question 37

How many cells form the blastocyst in rotational holoblastic cleavage?

Answer 37

32.

Question 38

When does cell compaction occur?

Answer 38

At the cell stage of rotational holoblastic cleavage we have compaction. This pulls the cells tighter together via cell-cell adhesion.

Question 39

What hormone is responsible for compaction?

Answer 39

E-cadherin.

Question 40

What process generates the blastocoel cavity in rotational holoblastic cleavage?

Answer 40

Cavitation?

Question 41

How does cavitation work?

Answer 41

there are sodium channels on the inner walls of the blastomeres. To generate the blastocoel, sodium is pumped into the space between the cells. This causes water to move in, to maintain osmotic balance. This inflates the space between the cells to make the blastocoel.

Question 42

What do the trophoblast cells form?

Answer 42

The placenta.

Question 43

What do the inner cell mass cells form?

Answer 43

The embryo

Question 44

In mammals, where does fertilisation occur?

Answer 44

At the fibrillated end of the oviduct.

Question 45

In mammals, where does cleavage occur?

Answer 45

As the organism moves up the oviduct to the uterus for implantation.

Question 46

Why does the blastocyst need to hatch?

Answer 46

The blastocyst must hatch from the zona pellucida to implant the uterine wall.

Question 47

Which enzyme helps the blastocyst to hatch?

Answer 47

Strypsin, is produced by the trophoblast cells.

Question 48

What is an ectopic preganancy?

Answer 48

When the pregnancy takes place in the ovary or oviduct.

Question 49

Discoidal cleavages occur in what kind of animals?

Answer 49

Fish and birds.

Question 50

In fish, egg and reptile eggs, where does the blastula develop?

Answer 50

On top of the yolk.

Question 51

In discoidal cleavage, what is the embryo called?

Answer 51

The blastodisc.

Question 52

What does the blastodisc look like?

Answer 52

A squashed ball of cells.

Question 53

What makes up the blastodisc?

Answer 53

The epiblast is the top. The hypoblast is the bottom.

Question 54

Is the cytoplasm of a blastodisc and the yolk continuous?

Answer 54

Yes.

Question 55

Superficial mesoblastic cleavage occurs in what animals?

Answer 55

Insects.

Question 56

What is special about superficial mesoblastic cleavage?

Answer 56

The zygote has a single nucleus and there is nuclear division without any cytoplasmic division. This results in a lot of nuclei. The nuclei then move out to the periphery of the cells. This is an example of synctium as the nuclei share a common cytoplasm. Once the nuclei have moved to the periphery we get a cytoplasm forming around each nucleus. This gives a cellular blastoderm.

Question 57

What happens once the nucei have moved to the periphery in superficial mesoblastic cleavage?

Answer 57

Once the nuclei have moved to the periphery we get a cytoplasm forming around each nucleus. This gives a cellular blastoderm.