The early embryo

Question 1

Graphical representation of the stages of development from oocyte to implantation

Answer 1

See additional sheet 7

Question 2

What day is the morula produced?

Answer 2

Day 4

Question 3

Define morula

Answer 3

The solid mass of blastomeres formed by cleavage

of a zygote.

Question 4

How is it determined where the first splitting occurs?

Answer 4

Sperm entry point

Question 5

How is the zygote cleavage ?

Answer 5

Cleavaged symmertically

See additional sheet 8

Question 6

How does frogs cleavage differ from humans?

Answer 6

After first division

The half with the sperm entry point develops into the actually zygote and the other half develops into the yolk sac.

Therefore, all subset cleavages will only occur in the half that will develop into the zygote

Question 7

Why does the frog embryo need to develop the yolk sac?

Answer 7

As its external fertilisation

Therefore needs a supply of food to develop until developed enough to gather its own food.

Question 8

What are the cells called after each division?

Answer 8

Blastomeres

Question 9

Does the zygote get bigger after each cleavage?

Answer 9

It does not

Instead the cells become smaller after each cleavage division.

Question 10

At what stage is not no longer a loosely arranged clump of cells?

Answer 10

8-cell stage

Question 11

What happens after the 3rd division?

Answer 11

The blastomeres maximise their contact with each other.

Forming a compact ball of cells held together by tight junctions.

Question 12

What are the differences and similarities between different organisms pregnancy?

Answer 12

Organisms develop at different rates

Therefore pregnancy is longer in humans than mice (9months to 9 days).

Looking at the stages of development there are similar characteristic events

Some critical differences (such as mice having a tail)

Question 13

What happens during compaction?

Answer 13

3 days after fertilisation, cells divide again producing a 16 cell morula.

Segregates inner cells and outer cells. Communication by gap junctions.

Question 14

What does the inner cells of the morula give rise to?

Answer 14

The tissues of the embryo

Question 15

What does the outer cells of the morula give rise to?

Answer 15

Forms the trophoblast

Later contributes to the placenta

Question 16

Define totipotent?

What cells are totipotent?

Answer 16

Can form all the cell types in a body.

Embryonic cells within the first couple of cell divisions after fertilisation are the only cells that are totipotent

After segreating inner cell and outer cell in the morula: no longer totipotent

Question 17

Define pluriopotent?

What are cells are pluriopotent?

Answer 17

Give rise to all of the cell types that make up the body.

Embryonic stem cells.

Question 18

Define multipotent?

Answer 18

Can develop into more than one cell type.

More limited than pluriopotent.

eg. adult stem cells.

Question 19

Graphic representation of the totipotency as the development of the zygote increases.

Answer 19

See additional sheet 9

Question 20

The embryonice germ layer and lineages?

Answer 20

See additional sheet 10

Question 21

What drives the first day of development?

Answer 21

The enzymes that have already been formed primer.

Question 22

What happens to gene expression during the 2nd cell stage?

Answer 22

Large burst of expression of the genes in the embryo.

All the genes- includes the non- important genes which will be silenced.

If this does not happen, the embryo will disintegrate.

Question 23

What are the 3 theories which determine the lineage of the cells?

Answer 23

1. Pre-packaged model
2. No determines
3. Hints of determines

Question 24

Name the transcription factors that are important for the generation of the first 3 lineages in the blastocyst

Answer 24

Oct4

Cdx2

Nanog

Gata6

Question 25

What transcription factors does the outer cell mass express?

Answer 25

Cdx2

Question 26

What transcription factors are expressed by the inner cell mass?

Answer 26

Oct4, Nanog and Gata6

Question 27

Why is it important that the expression of transcription factors between the outer and inner cell mass?

Answer 27

As it brings about a defining layer between them

Question 28

Graphical representation of the molecular circuit in developmental cleavage stage?

Answer 28

See additional sheet 11

Question 29

what happens with the morula enters the uterine cavity?

Answer 29

Fluid begins to penetrate through the zona pellucida into the intercellular space of the inner cell mass.

Question 30

what happens with the intercellular spaces becomes confluent (blended into one space)

Answer 30

A single cavity, the blastocele forms

Question 31

Why is the inside position of the zygot apolar?

Answer 31

Because the cells eventually are no longer defining and blend together