ANIMAL DEVELOPMENT : ANIMAL DEVELOPMENT THE STAGES OF EARLY EMBRYONIC DEVELOPMENT PREFORMATION vs EPIGENESIS: PREFORMATION vs EPIGENESIS FERTILIZATION: FERTILIZATION Creates diploid zygote
Triggers embryonic development
Sperm penetrates egg membranes, head is ingested, nuclei fuse.
Egg’s metabolic machinery is activated, meiosis is completed.
Egg raises barriers to entry of other sperm.
Fertilization membrane lifts off egg--‘slow block to polyspermy’
Acrosomal, Cortical Reactions: Acrosomal, Cortical Reactions Cortical Reaction: Fertilization Envelope: Cortical Reaction: Fertilization Envelope After Fertilization: After Fertilization Membrane lifted off zygote Cleavage Determinants: Cleavage Determinants Distribution of yolk
Even distribution (isolecithal)
Uneven distribution (telolecithal)
Holoblastic cleavage (mammals, frogs, sea stars)
Meroblastic cleavage (fish, birds, reptiles)
Deuterostome pattern Formation of a Blastula: Formation of a Blastula Cell division continues until a hollow ball of cells forms
One cell layer thick
Fluid filled space is a blastocoel
Indentation of blastopore ends this stage
Events of Gastrulation: Events of Gastrulation Three primary germ layers are established.
Basic body plan is established, including the primary body axes.
As a result of the movements of gastrulation, cells are brought into
new positions, allowing them to interact with cells that were
initially not near them. This paves the way for inductive
interactions, which are the hallmark of neurulation and
4. Archenteron may appear
Radial Cleavage: Radial Cleavage http://www.uleth.ca/bio/bio1020/images/star8.jpg Sea Star Sea Star Development: Sea Star Development http://www.uleth.ca/bio/bio1020/images/star8.jpg Blastula Gastrulation: Gastrulation archenteron Poles, Cleavage: Poles, Cleavage Frog Cleavage: Frog Cleavage FrogHoloblastic Cleavage: Frog Holoblastic Cleavage http://www.uleth.ca/bio/bio1020/images/frog12.jpg Frog Blastula: Frog Blastula http://www.uleth.ca/bio/bio1020/images/frog10.jpg Gastrulation: Gastrulation http://www.uleth.ca/bio/bio1020/images/frog8.jpg archenteron Neurulation: Neurulation http://www.uleth.ca/bio/bio1020/images/frog5.jpg Rate of Cell Division: Rate of Cell Division EARLY CLEAVAGE 2-64 cells: EARLY CLEAVAGE 2-64 cells Morula Blastula: Morula Blastula 16-64 cells 128 cells
Blastocoel 256 cells Development in a Chick Embryo: Development in a Chick Embryo http://www.lawrence.edu/dept/biology/embryoatlas/stage18whole1.jpg Neurulation in a Chick (24 hr): Neurulation in a Chick (24 hr) http://www.uoguelph.ca/zoology/devobio/24hrchck/24ck2.htm Chick Embryo 72 hrs: Chick Embryo 72 hrs http://www.uoguelph.ca/zoology/devobio/72hrchck/72ckintr.htm