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Developmental Biology. > Cleavage. > Flashcards

Cleavage. Flashcards

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1
Q

Cleavage is characterised by what?

A

Rapid cell divisions.

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2
Q

When does transcription in the cleavage stage occur?

A

About 1/2 way through.

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3
Q

What drives transcription in the early stages of transcription?

A

Maternal mRNAs.

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4
Q

What are the 5 types of holoblastic cleavage?

A

Radial.

Unequal.

Spiral.

Bilateral.

Rotational.

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5
Q

Cleavage patterns are usually determined by what?

A

The amount of yolk in the egg.

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6
Q

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

A

The genes of the organism.

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7
Q

What kind of eggs have holoblastic cleavage?

A

Isolecithal and mesolecithal eggs have holoblastic cleavage.

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8
Q

What does holoblastic cleavage look like?

A

The cleavage plane will penetrate through the entire egg.

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9
Q

What type of eggs have mesoblastic cleavage?

A

Telolecithal and centrolecithal eggs have mesoblastic cleavage.

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10
Q

What does mesoblastic cleavage look like?

A

The cleavage planes do not penetrate through the yolk.

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11
Q

What is a morula?

A

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

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12
Q

How many cells are needed to make a blastula?

A

More than 128.

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13
Q

What are the 2 types of mesoblastic cleavage?

A

Discoidal.

Superficial.

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14
Q

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

A

All the same size.

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15
Q

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

A

Radial symmetry.

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16
Q

What organism does radial holoblastic cleavage take place in?

A

The sea cucumber.

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17
Q

What kind of cleavage do sea urchins undergo?

A

Sea urchins undergo unequal holoblastic cleavage.

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18
Q

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

A

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

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19
Q

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

A

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

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20
Q

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

A

8 mesomeres.

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21
Q

What do the mesomere cells form?

A

The ectoderm.

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22
Q

What kind of cleavage occurs in amphibians?

A

Unequal radial holoblastic cleavage.

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23
Q

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

A

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.

24
Q

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

A

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.

25
Q

What kind of cleavage occurs in snails and molluscs?

A

Spiral holoblastic cleavage.

26
Q

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

A

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

27
Q

How does the tilt occur?

A

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.

28
Q

The direction of the cleavage tilt is determined by what?

A

The genotype of the mother.

29
Q

In spiral holoblastic cleavage does a blastocoel form?

A

No.

30
Q

Bilateral holoblastic cleavage occurs in which organism?

A

Tunicates.

31
Q

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

A

1.

32
Q

Rotational holoblastic cleavage occurs in which organisms?

A

Mammals.

33
Q

How does rotational holoblastic cleavage occur?

A

Blastomeres divide in different ways.

The 1st cleavage is meridional.

The 2nd is meridional in 1 blastomere and equatorial in the other.

34
Q

What is the outer layer of a blastocyst called?

A

The trophoblast.

35
Q

What is the inner layer of a blastocyst called?

A

The inner cell mass.

36
Q

How many cells form the morula in rotational holoblastic cleavage?

A

16.

37
Q

How many cells form the blastocyst in rotational holoblastic cleavage?

A

32.

38
Q

When does cell compaction occur?

A

At the cell stage of rotational holoblastic cleavage we have compaction.

This pulls the cells tighter together via cell-cell adhesion.

39
Q

What hormone is responsible for compaction?

A

E-cadherin.

40
Q

What process generates the blastocoel cavity in rotational holoblastic cleavage?

A

Cavitation?

41
Q

How does cavitation work?

A

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.

42
Q

What do the trophoblast cells form?

A

The placenta.

43
Q

What do the inner cell mass cells form?

A

The embryo

44
Q

In mammals, where does fertilisation occur?

A

At the fibrillated end of the oviduct.

45
Q

In mammals, where does cleavage occur?

A

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

46
Q

Why does the blastocyst need to hatch?

A

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

47
Q

Which enzyme helps the blastocyst to hatch?

A

Strypsin, is produced by the trophoblast cells.

48
Q

What is an ectopic preganancy?

A

When the pregnancy takes place in the ovary or oviduct.

49
Q

Discoidal cleavages occur in what kind of animals?

A

Fish and birds.

50
Q

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

A

On top of the yolk.

51
Q

In discoidal cleavage, what is the embryo called?

A

The blastodisc.

52
Q

What does the blastodisc look like?

A

A squashed ball of cells.

53
Q

What makes up the blastodisc?

A

The epiblast is the top.

The hypoblast is the bottom.

54
Q

Is the cytoplasm of a blastodisc and the yolk continuous?

A

Yes.

55
Q

Superficial mesoblastic cleavage occurs in what animals?

A

Insects.

56
Q

What is special about superficial mesoblastic cleavage?

A

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.

57
Q

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

A

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

Developmental Biology. (21 decks)

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