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• Embryology - study of development of the embryo
5 major stages..
1. Gametogenesis - gamete production 2. Fertilization - gamete --> zygote3. Cleavage - Zygote --> Blastula4. Gastrulation - Blastula --> Gastrula5. Organogenesis - Organ Formation
-i.e. Neurulation- Gastrula --> Neurula
Animal Development
Fertilization
Sperm must pass through 3 barriers
• 1. Jelly coat• 2. Vitelline layer• 3. Plasma membrane
Fertilization-male and female gametes fuse to form a zygote
Fertilization
• Acrosome cap -contains digestive enzymes that eat away at jelly layer
1. Sperm attaches the jelly coat of the egg
Fertilization
2. Sperm reach vitelline envelope
• Vitelline layer-species-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 occurs-sperm 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
• Embryology - study of development of the embryo
5 major stages..
1. Gametogenesis - gamete production 2. Fertilization - gamete --> zygote3. Cleavage - Zygote --> Blastula4. Gastrulation - Blastula --> Gastrula5. Organogenesis - Organ Formation
-i.e. Neurulation- Gastrula --> Neurula
Animal Development
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
• Embryology - study of development of the embryo
5 major stages..
1. Gametogenesis - gamete production 2. Fertilization - gamete --> zygote3. Cleavage - Zygote --> Blastula4. Gastrulation - Blastula --> Gastrula5. Organogenesis - Organ Formation
-i.e. Neurulation- Gastrula --> Neurula
Animal Development
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
• Embryology - study of development of the embryo
5 major stages..
1. Gametogenesis - gamete production 2. Fertilization - gamete --> zygote3. Cleavage - Zygote --> Blastula4. Gastrulation - Blastula --> Gastrula5. Organogenesis - Organ Formation
-i.e. Neurulation- Gastrula --> Neurula
Animal Development
NeurulationNeurulation – 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
Neurulation1. 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
Neurulation2. Neurulation complete - Neurula
formedNeurula- 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
• Embryology - study of development of the embryo5 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
Animal Development