Organismal Development
Part 5
Animal Development and
Embryology
Crashcourse Video
• https://www.youtube.com/watch?v=k_9MTZg
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Cytoplasmic Determinants
DNA controls the process of development in
animals through the production of specific
proteins and enzymes.
1. Cytoplasmic determinants – proteins
produced in the cytoplasm that regulate
mitosis and cell development.
2. Pattern genes – control the basic pattern
of an organism. Ex. Frog, sponge, snake,
human.
3. Positional genes – control the position of
various structures throughout the
developing organism. Ex. Brain, bones,
skin, muscles.
Early cells are considered totipotent. This means that they have the ability to turn into
any other type of cell in the developing organism. As development progresses, cells
begin to differentiate based on cell signals and DNA.
Apoptosis in the hand
Apoptosis – the programmed death of cells to create certain structures in the developing
organism. In humans, we see this most commonly in our hands, feet, and the separation of
important organs and other structures in the body.
Failed Apoptosis with Hands
Failed Apoptosis with toes
Failed Apoptosis with the Tongue
Cleavage
Cleavage – rapid cell growth as
development continues that leads to the
creation of a blastula.
Cells get smaller with each division, but the
overall ball of cells stays the same size. Cells
do not go through normal G1 and G2. Only
S phase and M phase.
Steps of Cleavage in Animals
• 1. Blastulation – during this stage of development,
cells continue to divide to create a hollow ball of cells
called the blastula.
– Two cell layers thick
– Animal pole becomes head, vegetal pole becomes body.
• 2. Gastrulation – during this stage of development,
the hollow ball of cells begins to pinch in, creating a
gastrula.
– Three cell layers thick
– Starting to create the mouth and anus.
Animal vs Vegetal Poles of a Blastula
Morula, Blastula, Gastrula
Endoderm, Mesoderm, Ectoderm
Three tissue layers of a
developing organism.
1. Ectoderm – this layer of cells
forms the skin and the CNS.
2. Mesoderm – this layer of
cells forms the muscles,
bones and kidneys.
3. Endoderm – this layer of
cells forms the digestive
tract organs, lungs and
bladder. This is the tube
that runs through the center
of most organisms!
Embryo
Formation of the Embryo
Different types of development
• Dueterostomes - The anus is made first, and
development moves towards the mouth.
– Ex. Humans, fish, reptiles, starfish
• Protostomes – The mouth is made first, and
then development moves towards the anus.
– Ex. Arthropods, mollusks, worms