Download Cell Differentiation

Embryonic Development
 Gametes (eggs/sperm) are produced by what process?
Meiosis
 Egg + Sperm = Zygote ---> Embryo (multicellular)
 The zygote (one fertilized cell) becomes trillions of
highly specialized cells by what process? Mitosis
Zygote  Embryo
What happens to the size of individual cells as the zygote
undergoes Mitosis to produce a multicellular embryo?
Two main stages of Embryonic Development:
1. Cleavage - Zygote undergoes rapid cell division
(Mitosis) to produce a multicellular hallow ball of
cells called a blastula (about 100 cells).
 Cleavage helps to organize the embryo into
developmental regions.
o The position of each new cell in the
embryo promotes expression of particular
groups of genes
 Chemical signals in the cytoplasm
activate specific genes and directs
development.
o A particular cell only expresses genes that
code for proteins with a function in that
cell or that need to be produced by that
cell.
 Only some genes activated in each cell.
Embryo Implantation
2. Gastrulation – During this stage of development the
embryo accumulates more cells and the cells sort into
three layers. The embryo is now called the Gastrula.
 As the embryo develops, individual cells undergo
Cellular Differentiation – becomes specialized in
their structure and function.
 Three Embryonic Tissue Layers:
o Ectoderm – Forms from the outer layer of
the gastrula.
 Develops into the outer skin of the
organism and its nervous system
o Endoderm – Forms from the embryonic
digestive tract.
 Develops into the inner lining of the
digestive tract and lungs
o Mesoderm – Forms from the space between
the ectoderm and endoderm.
 Develops into most other organs
Differentiation Flow Chart
Egg
+
Sperm
Zygote
Blastula
Gastrula
Gastrulation
Fertilization
Cleavage – rapid
mitotic divisions.
Embryo – 9
weeks
* 50 days after
fertilization
* Ball of 100 cells
* Fluid filled
* Outer layer –
called trophoblast
* Inner cells called Inner cell
mass (Stem cells)
* Formation of 3
cell layers:
1. Ectoderm –
outer layer (skin
and central
nervous system)
2. Endoderm –
Digestive tract and
lungs.
3. Mesoderm –
most other organs
60 days