09 Molecular Basis Of Development (Part 1)

09 Molecular Basis Of Development (Part 1) - 1 Molecular...

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1 Molecular Basis of Development  and the Evolution of Development Created by Jason Mayberry for Bio200, Evolutionary Biology University at Buffalo, Fall 2007
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Goals 1. Understand how patterns of gene expression lead to  morphological changes contributing to a phenotype 2. Understand specific examples of how important  developmental genes have contributed to the  evolution of animal form (phenotype)
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Differentiation Patterning Concepts Underlying Development Initial cells which are perfectly identical give rise to all the different cell types found in the body. After Fertilization, the embryo divides by Mitosis to produce billions of genetically identical cells. How does an organism form from a clump of cells which are all identical? Two major developmental concepts work in unison to produce an organism. Inner Cell Mass Trophoblast Ectoderm Mesoderm Endoderm Placenta Membranes Skin Nerve and   Neuroendocrine Kidney and  Gonads Muscle, Blood,  Spleen, Bone  GI Tract Internal Organs Gametes Gastrulation Spatial Orientation (Polarity) Tissue Locations and Boundaries Size (Mitosis) Morphogenesis Top Bottom Front Back Right Left
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Differentiation Potency :  The ability of a cell to give rise to different  cell types. Commitment :  As cells move towards a specific fate  they go through degrees of  dedication  to and  development towards their fate As cells become more and more committed to a  specific fate they lose potency (these are opposite  sides of the same coin) Differentiation :  Process by which a cell actually  becomes what it is supposed to be (produces functional  proteins, etc.) Totipotent :  can give rise to  all cell types Pluripotent ::  can give rise to  any embryonic cell type (Inner  Cell Mass) Multipotent :  can give rise to  limited set of cell types Specified :  makes reversible  progress toward a fate Determined  (committed) :   makes irreversible progress Differentiated :  the cell has  become what it is supposed to  be Inner Cell Mass Embryonic Stem Cells Trophoblast Placenta Mem- branes Skin Nerve,  Neural  Endo- crine  Organs Kidney,  Gonad Muscle,  Blood,  Spleen,  Bone GI  Tract Internal  Organs Gametes Blastocyst Fertilization Morula Ectoderm Mesoderm Endoderm Gastrulation “It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life” L ewis Wolpert (1986) Note, more than one descriptor usually  applies to a cell.  For instance, a cell may  be multipotent but be determined to  become a blood cell of some type.  
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Stem Cells vs. Differentiated Cells Limited number of cell divisions possible Infinite ability to divide (immortal) Cell Division Embryonic Stem cells   Cells derived from  early divisions of the  fertilized oocyte
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