• 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

Starfish Development

BlastulaBlastopore

Blastocoel

GastrulationBlastopore –

becomes the anus

Archenteron

Mouth

Anus

Frog Development

Cell size difference

Yolk Plug

Chicken Development