ch.47 animal development
TRANSCRIPT
Animal DevelopmentChapters 21 & 47
“Homunculus”
Acrosomal & Cortical Reactions
Cortical Reaction: Wave of Ca+
(So only one sperm gets in)
Preventing Cross-Species Fertilization
• Fertilin protein in sperm fits like a key into a recognition protein on egg
CleavageNote: Size is not increasing
Early Development Stages
• Single cell• Cleavage
– Produces smaller cells– Total size does not increase
• Morula – 16 to 64 cells• Blastula – at least 128 cells• Gastrula – formation of blastopore
– Formation of germ cell layers• Ectoderm, endoderm, mesoderm
– Primitive gut
Sea Urchin Development
Cleavage Stages: rapid mitosis without growth
• Reduces cell size.• All cells receive identical copy of DNA.• Cytoplasm they inherit is not identical,
may contain special substances (determinants: beginning of cell differences).
• Forms mass of cells (morula), then hollow ball called (blastula)
Cleavage in Vertebrate Embryo
Blastula
Gastrulation
Some key stages of development in animals and plants
Review: What are the stages?
Organogenesis• Formation of organs
• 3 kinds of morphogenic changes– Folds– Splits– Dense clustering of cells
• First to develop– Neural tube– Notochord– Skeletal rod
Neurulation
Organogenesis of Chick EmbryoRudimentary organs have formed (56 hours)
Eye
Forebrain
Heart
Somites
Neural Tube
Amniotic Egg & Development ofExtraembryonic Membranes
Human Embryo & Extraembryonic Membranes
• Blastocyst – hollow ball of cells• Trophoblast
– epithelium of blastocyst– Enzymes - implantation– Forms placenta
• Chorion – develops from trophoblast– Outer membrane
• Amnion – develops from epiblast– Fluid-filled cavity
• Yolk sac – blood formation• Allantois – umbillical cord
Extraembryonic Membranes• Amnion• Yolk sac• Chorion• Allantois
Functions of the Placenta
• Fetal blood vessels penetrate pools of maternal blood in endometrium
• Blood does NOT mix, but O2 and CO2 glucose/vitamins diffuse across
• Prevents passage of most large proteins & cells.
Morphogenesis & Changes in Cell Shape
Morphogenesis &Convergent Extention of Cell Sheets
• Cells rearrange themselves
• Narrower & longer
Major Stages of Embryogenesis
Genetic Basis of Development
How do you get from one cell to a multi-cellular animal?
Stem Cells: Undifferentiated Cells
When a cell divides, the new cells don’t get the same stuff
& cells can affect their neighbors
Determination & Differentiation
Segmentation genes are turned on in certain cells
Hox Genes: head to tail organization in animals
Switches
Apoptosis: programmed cell death
Let’s discuss the role of these during development:
• Hox genes• Organizer• Noggin• Sonic hedgehog• ZPA• Switches
Uh oh… How does this happen?
How does this happen?
How does this happen?