Animal Development Emily Huang, Erin McGrath, Michelle Xu.
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Transcript of Animal Development Emily Huang, Erin McGrath, Michelle Xu.
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Animal Development
Emily Huang, Erin McGrath, Michelle Xu
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Review• Cell differentiation• Morphogenesis
• Blastula• Gastrulation• Cytoplasmic determinants
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Fertilization
• Sperm + egg combine to form diploid (zygote)– Contact of sperm to surface of egg initiates
metabolic reactions within egg that trigger onset of embryonic development• Acrosomal Reaction• Cortical Reaction
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Fertilization In Different Species
Mammal-internal fertilization-eggs coated in follicle cells-fusion doesn’t not occur until after first cell division (12-36 hours)
Echinoderm-external fertilization-eggs have a jelly coat-nuclei of sperm and egg fuse immediately-first cell division occurs 90 minutes after fusion
Similarities-contact, acrosomal reaction (dig hole into egg), fusion of sperm and egg membranes, complete entry of sperm, cortical reaction blocks other sperm from coming in-sperm cell contains basal body which becomes the centrosome and allows zygote to split
Differences
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After Fertilization…
• …embryonic development proceeds through cleavage, gastrulation, and organogenesis.– Stage 1: cleavage cell division creates a hollow
ball of cells (blastula) from the zygote– Stage 2: gastrulation produces 3 layered embryo
(gastrula)– Stage 3: organogenesis generates rudimentary
organs from which adult structures grow
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Cleavage• Blastomeres: smaller cells that result from cleavage, each with its own nucleus• First 5-7 divisions form a cluster of cells known as the morula• Blastocoel: fluid filled cavity that begins to form within the morula• Yolk: stored nutrients, most concentrated toward one pole, the vegetal pole
and decreases toward the animal pole• Afterwards, gastrulation occurs
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Gastrulation• Dramatic rearrangement! • Forms primitive gut• Driven by changes in cell motility, cell shape, and cellular adhesion to other cells and e.c. matrices • 3 layers produced- collectively the gastrula• Germ layers: ecto, meso, endo
Sea Urchins: Frogs:
Chicks:
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Germ Layer Fun
ECTODERM:-skin (sweat glands, hair follicles)-sensory receptors in epidermis-cornea, lens of eye-nervous system-tooth enamel
MESODERM:-skeletal system-muscular system-excretory system-circulatory and lymphatic systems-reproductive system-dermis of skin
ENDODERM:-epithelial lining of digestive tract and respiratory system-lining of urethra, urinary bladder, repro. system-liver, pancreas, thymus, thyroid
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Organogenesis
FrogChick
When the three germ layers begin to develop into organs
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Development Adaptations of Amniotes
• Reptiles, birds, and mammals are called amniotes.
• All vertebrate embryos require aqueous environment, so animals use fluid filled eggs or uteri
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Extraembryonic Membrane
• Present in mammals, birds and reptiles.• In birds and reptiles: germ layers develop into– Amnion- contains the fluid and fetus– Yolk sac, chorion, and allantois
• Allantois is a disposal sac for waste• Yolk sac expands over yolk, stockpile of nutrients• Exchange gases between embryo and surroundings
• These structures provide “life support system”• Mammals have the same structures, only we have a
uterus instead of an egg to contain them
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USTHEM
(chicken)
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Morphogenesis
• Cytoskeletons in animals cells allow them to “crawl” from place to place in all developing animals.
• Cell crawling changes the shape of the developing animal by extending or contracting- convergent extension
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What affects developmental fate?
• Cytoplasmic determinants cell differentiation• Interactions among cells causes changes in gene
expression “induction”
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Limb Formation and Spatial Organization
• Inductive signals play a major role in pattern formation
• Positional information: molecules that direct a cell to its correct location in the body
• In all animals with limbs: apical ectodermal ridge (AER), zone of polarizing activity (ZPA)
• They are major limb bud organizers
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• apical ectodermal ridge (AER)- a thick ridge of ectoderm at the tip of a bud of a limb, determines growth of the limb
• zone of polarizing activity (ZPA)- sprouts from the mesoderm, forms the digits
• ZPA excretes a protein growth factor called SONIC HEDGEHOG!!!!!!!!!!!!!!
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• THE END <3