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Transcript of Animal Development
Development continues unti maturity Fertilization Cleavage Gastrulation External Development of frog eggs Internal Development of a Dog Embryo Yolk Umbillicus/Placenta The evolution of the amniotic egg was a major adaptation that allowed reptiles (and subsequently birds & mammals) to spend their entire lifecycle on land. Four membranes:
Amnion: Protect fetus
Chorion: Gas Exchange
Allantois: Waste Storage
Yolk: Food Source Fertilization events in sea urchins Sperm releases enzymes from acrosome at tip to penetrate jelly coat of ovum
Fusion of sperm and ovum triggers the formation of an mostly impenetrable "fertilization envelope" by an immediate cortical reaction.
This is the "Fast Block" The fusion of gametes triggers a massive wave of Calcium ion release across the ovum membrane.
This prevents any other sperm from entering the ovum ("polyspermy").
The process takes 30 seconds
This is the "Slow Block" Fertilization events in mammals Differences?
No Fast Block The fertilized cell is a "zygote" The zygote divides... And divides... And divides again, and again Eventually, it's a "morula" Then, it's a "blastula" "Inner cell mass" n + n = 2n "splitting" "organization" Early gastrulation Mid gastrulation Complete Gastrula Details may vary, but Gastrulation is crucial.
The three primary germ layers will be established.
All tissues and organs will come from these germ layers.
The primitive gut tube ("archenteron") will form. Gastrulation in Sea Urchins Gastrulation in Frogs Just Think Layers Protostomes vs. Deuterostomes A major division line among animals.
Deuterostomes: Chordates, Echinoderms
Protostomes: Everyone else
Direction of cleavage
Fate of blastopore during gastrulation "getting fancy" Neurulation & Organogenesis Neurulation: The development of the primitive notochord (in chordates, obviously)
Organogenesis: The development of "somites", patches of cells which will give rise to organs Neurulation begins with the infolding of the neural plate.
After the neural tube is formed, somite formation is initiated Neurulation in a frog embryo Organogenesis in a chicken embryo Morphogenesis: Changes in cell shape during development are referred to as "morphogenesis".
This is a very important aspect of developmental biology (structure and function relationships).
Cells can do all sorts of neat things due to changing shape. Convergent Extension: Polarity & Cell Fate Experiments "what goes where and how it's done" One of the major developmental questions:
How do cells know where they are in the embryo, and what they should become?
Roughly: Cues from two main sources-
uneven distribution of protein molecules
signals from nearby cells ("induction") Unequal distribution of proteins in an early stage C. elegans embryo Fate mapping: done by staining cells in early stage embryos Fate map of the C. elegans embryo (intestine map shown) Funky Frog Fetuses:
By manipulating frog embryos at early stages of development, polarity is disturbed Removal of a specific region (the "gray crescent"), leads to an embryo lacking dorsal structures Transplantation of a specific region (dorsal lip) leads to a duplication of the embryo in opposite polarity. Limb Development:
Chicken limb development is dependent upon specific "organizer regions" Transplantation of the organizer region (ZPA) leads to limb duplication. Fates of the three primary germ layers (learn this!) Urchin Larvae How does a multicellular organism develop from a zygote?
How is the position ("polarity") of the parts of an organism determined?
How does differentiation of cell type occur in animals? Big Questions Can You Explain the major phases of animal development.
Demonstrate how differentiation, induction, and morphogenesis all function in development.
Explain the causes and effects of developmental disruptions. And Away We Go At this point, each cell can still become a whole organism ("totipotency") All "Blue" light micrographs depict sea urchin embryos Frog embryo shown Cleavage in a frog embryo Gastrulation in a sea urchin Gastrulation & Neurulation in a frog Early Idea: Preformation
Little man (homunculus) inside sperm Things happen pretty fast...in sea urchins Polarity and Body Axes
Animal and vegetal poles
First cleavage divides the gray crescent
All body directions set
More on this later... Meroblastic Cleavage
Birds, other reptiles, fish Gastrulation in Chicks 3 Common Model Organisms Sea Urchin
Chicken What about humans? We are amniotes Eggs adapted to dry land
Extra-amniotic membranes Wait......
Humans don't have egg shells...