LEC.164 Lecture 2

Cleavage

Divisions of fertilized egg into cells, differentiation begins

Body axis

anterior-posterior/dorsal-ventral/left-right

Gastrulation

Establishing gut and germ layers

\-cells move around embryo

Determination

What the cell is going to specialise into is decided

What does the blastula represent

The end of cleavage

What is the blastula

A hollow, fluid filled ball of cells

Gastrulation

Blastopore starts to form

What is seen in gastrulation

Blastocoel, endoderm, ectoderm, archenteron, blastopore

What are the smaller cells created during cleavage caused

Blastomeres

What are the different types of cleavage

holoblastic and meroblastic

what is holoblastic cleavage

complete division, eggs with small/moderate types of yolk

what is meroblastic cleavage

incomplete division, eggs with large yolks (preventing separation)

what type of cleavage do echinoderms do

holoblastic, planar division rotations

at what size can a space be seen in sea urchins

32 cells

Where does the majority of animal body derive from?

Divisions towards the animal pole

Where are more cells produced. Away from or close to yolk?

Away from the yolk

Xenopus 3rd cleavage

asymmetric, forms unequally sized blastomeres

What forms on top of the yolk

A disk of cells

What is superficial cleavage

Cleavage on the surface but not on the inside (where yolk is present)

What type of cleavage happens in mammals

Rotational on perpendicular planes

What is the end point of cleavage

The morula

Inner cell mass

the inner 8 cells

trophectoderm

the outer \~20 cells

what does the ICM form

the embryo

what does the trophectoderm become

the extra-embryonic tissues

when/where are the trophectoderm and icm established

in the blastocyte before implantation

Cleavage definition

rapid, synchronous cell division with no increase in embryo size

Order of cell division with growth

M, G1, S, G2

Why is cell division in cleavage faster

No growth/gap phases