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Published byHester Willis Modified over 6 years ago
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Development Sea urchin Deuterostome Isolecithal Holoblastic cleavage
Chick Deuterostome Telolecithal Meroblastic cleavage Fertilization cleavage Blastulation & gastrulation Organogenesis & pattern formation Why do cells move in specific ways at specific times? How, why, and when do cells become specialized?
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Sea urchin body plan © 1997 Chris Patton, Stanford University
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Sea urchin fertilization
acrosome Cortical granules Fertilization membrane
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© 1997 Chris Patton, Stanford University
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Fertilization
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Holoblastic--cleaves completely through cell
Isolecithal--evenly dispursed yolk.
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Sea Urchin Cleavage and blastulation
3 div. 8 cell 1st div. Hatched blastula blastula
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Three types of morphogenetic movements during
gastrulation.
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Gastrulation -2 types of morphogenetic
movements. Ingression of ~40 cells to form Primary mesenchyme cells (PMC) Formation of mesoderm.
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Gastrulation 2. Invagination of cells at vegetal pole Forms blastopore and archenteron-primitive gut 3 germ layers ectoderm- skin and nervous system. mesoderm- bone, muscle, circ. system, internal organs. endoderm- stomach and guts. archenteron
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Together=mesoderm 2nd ingression of cells to form Secondary mesenchyme
Primary mesenchyme
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2nd invagination at animal pole
to form mouth Complete gastrula Germ layers Ecto Meso Endo archenteron
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Sea urchin larval development.
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Sea urchin larva
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Chick Telolecithal-asymmetric 3rd 2nd 1st div. 4th
shell Chick Shell membrane albumen Nucleus Cytoplasm Yolk Telolecithal-asymmetric 3rd 2nd 1st div. 4th Meroblastic cleavage-part cleavage
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~100,000 cells when egg laid. Epiblast - 3 germ layers ectoderm mesoderm endoderm
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Delamination
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Ingression- mesoderm
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Chick gastrulation. Primitive streak -cells ingress
-induced by hypoblast ~blastopore Notochord -induced by Hansen’s node Somites -muscle, bone Embryo lifts off surface- 3 layers- ectoderm mesoderm endoderm Becomes brain Sacs form around embryo
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Fresh laid egg-blastodisc
13 hour egg
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24 hour chick sections
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33 hour chick sections
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33 hour whole mount
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48 hour 72 hour
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Mosaic vs. Regulative Development
Mosaic - after each cleavage, cells have specific fates. Regulative - cell communicate and can change their fate. Induction Studies can lead to discovery of hormones, regulatory genes. Defects in the normal processes are the basis of many cancers and developmental birth defects.
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Horstadius experiments-
Show that there are mosaic and regulative Aspects to sea urchin development. Split egg Separate 8 cells In half
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Pattern formation - mesoderm induces ectoderm to make either a leg or wing
But ectoderm determines which. AER = apical ectodermal ridge.
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