Animal Development
• Embryology - study of development of the
embryo
5 major stages..
1. Gametogenesis - gamete production
2. Fertilization - gamete --> zygote
3. Cleavage - Zygote --> Blastula
4. Gastrulation - Blastula --> Gastrula
5. Organogenesis - Organ Formation
-i.e. Neurulation- Gastrula --> Neurula
Fertilization
Fertilization-male and female gametes fuse to
form a zygote
Sperm must pass
through 3 barriers
• 1. Jelly coat
• 2. Vitelline layer
• 3. Plasma membrane
Fertilization
1. Sperm attaches the jelly coat of the egg
• Acrosome cap contains digestive
enzymes that eat
away at jelly layer
Fertilization
2. Sperm reach vitelline envelope
• Vitelline layerspecies-specific
boundary involved
in sperm-egg
recognition
• ensure other
species cannot
fertilize the egg
Fertilization
3. Sperm /egg plasma membrane fuse
• Sperm nucleus
enters the egg
• Fertilization occurssperm nucleus and
egg nucleus form a
2N zygote
Fertilization
4. Prevention of Polyspermy – entrance of
multiple sperm
• 1.Change of electrical potential of the
egg plasma membrane- fast
• 2.Confusion of sperm- Egg releases all
of their Ca ions
• 3.Cortical reaction- slower, mechanical
block, initiated in response to Ca
release
Fertilization
• Cortical granules - reside just below of plasma
membrane
• Cortical reaction – under high Ca levels granules
release contents between plasma and vitelline
membrane, causes water to rush in
• Vitelline layer - hardens and separates from the plasma
membrane= fertilization membrane formed
Animal Development
• Embryology - study of development of the
embryo
5 major stages..
1. Gametogenesis - gamete production
2. Fertilization - gamete --> zygote
3. Cleavage - Zygote --> Blastula
4. Gastrulation - Blastula --> Gastrula
5. Organogenesis - Organ Formation
-i.e. Neurulation- Gastrula --> Neurula
Cleavage
• Cleavage-rapid
succession of cell
division
• doubling with each
division
• each cell smaller than
zygote
• Blastula- multi-cellular
embryo formed from a
single celled zygote
Cleavage
• Blastula- hollow
ball of cells with a
large cavity
surrounded by one
or more layers of
cells
• Blastocoel – fluid
filled cavity forms at
the center of
embryo
Animal Development
• Embryology - study of development of the
embryo
5 major stages..
1. Gametogenesis - gamete production
2. Fertilization - gamete --> zygote
3. Cleavage - Zygote --> Blastula
4. Gastrulation - Blastula --> Gastrula
5. Organogenesis - Organ Formation
-i.e. Neurulation- Gastrula --> Neurula
Gastrulation
Gastrulation - sorts all the cells into distinct cell
layers (ectoderm, endoderm, and mesoderm)
Blastula (hollow ball of cells)
transformed into the Gastrula (three
layered stage)
Gastrulation
1. Gastrulation begins- Blastopore formed
Blastopore - midway opening on one side
of the blastula
• Site of cell migration
from the surface
into the interior
• Future site of anus
Gastrulation
2. Cell migrating to form layers
• Archenteron –
primitive gut formed
(endoderm)
• future mouth
Gastrulation
3.Gastrulation complete - Gastrula formed
•
Endoderm and archenteron -replace the blastocoel
•
Mesoderm - forms a layer between the ectoderm and endoderm
•
Ectoderm- forms the outer layer except for a cluster of endodermal
cells (yolk plug)
•
Yolk plug- (endoderm) marks the site of the blastopore and of the
future anus
Animal Development
• Embryology - study of development of the
embryo
5 major stages..
1. Gametogenesis - gamete production
2. Fertilization - gamete --> zygote
3. Cleavage - Zygote --> Blastula
4. Gastrulation - Blastula --> Gastrula
5. Organogenesis - Organ Formation
-i.e. Neurulation- Gastrula --> Neurula
Neurulation
Neurulation – embryonic formation of the
neural tube directed by the underlying
notochord
• Notochord- stiff rod
(mesoderm) runs down the
back of the embryo
provides support for other
developing tissues
• -Future backbone
Neurulation
1. Neurulation begins neural tube formation
• Neural plate –
thickened region
(ectoderm) arises a pair
of pronounced ridges
called the neural fold
• Neural tube – formed
when neural folds meet
• future brain and spinal
cord
Neurulation
2. Neurulation complete - Neurula
formed
Neurula- an embryo with a neural
tube
• Somites-internal segmented
structures (mesoderm)
• Give rise to vertebrae and
associated muscles of the
backbone
• Coelom – body cavity (mesoderm)
developed next to somites
Animal Development
• Embryology - study of development of the embryo
5 major stages..
1. Gametogenesis - gamete production (i.e. Meiosis)
2. Fertilization - union of sperm & egg cell --> 2n zygote
3. Cleavage - rapid succession of cell divisions forms
hollow ball of cells called BLASTULA embryo
4. Gastrulation - period of cell migrations as BLASTULA
embryo converted into a 3 layered stage called
GASTRULA embryo
5. Organogenesis - Organ Formation
-i.e. Neurulation- Gastrula --> Neurula
Starfish
Development
Blastocoel
Blastopore
Blastula
Archenteron
Blastopore –
Gastrulation
becomes the anus
Mouth
Anus
Frog Development
Cell size difference
Yolk Plug
Chicken Development