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EarlyDevelopmental Stages
ofAnimals
Fertilization- the combining of a sperm with an
egg
the result is called a zygote
Pictures of Zygotes
frog human
Early Cell Divisions
early cell divisions are called cleavage
- the zygote cleaves to become 2, 4, & 8 cells
Pictures of 2 Cell Stage
Pictures of 4 Cell Stage
8 cells become 16 cells
8 cells 16 cells
cleavage
the 16 & 32 cell stage is called a morula
morula
Pictures of 16 celled Morula
After several more divisions, the stage is called a blastula.
The entire process of changing from a zygote to a blastula is called blastulation.
Blastulationzygote blastul
a
blastulation
The Blastula
Pictures of Blastula
Review of Blastulation
A. 1 cellB. 2 cellsC. 4 cells
D. 8 cellsE. morulaF. blastula
Gastrulation- a blastula becoming a
gastrula
Gastrulation
Gastrulation starts with the folding in of cells at a spot called the blastopore.
The result is a cavity “gut” that will become the digestive system and 2 or 3 cell layers (called “germ” layers).
Result of Gastrulation
gutectoderm
endodermmesoder
m
- skin and nervous systemEctoderm
Endoderm- digestive
systemMesoderm- other organs and body
systems
Pictures of Gastrula
blastopore
Protostomes vs. Deuterostomes
Embryo Development
The term “embryo” is used to describe all stages of development until you can tell what the organism is going to be.
Human embryosweek 4 week
5
Fetus Development
Once you can tell what organism it will be, it is called a “fetus”.
Zygote Morula Blastula
GastrulaLarva
Fetus
Adult
Adult
(if in water)
(if on land or in mother)
Summary of Development
- the term “embryo is usually used for any stage of development
The End