CH47Animal Development

CH47Animal Development -...

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CHAPTER 47:  ANIMAL  DEVELOPMENT Alicia LaHatte, Jesse Lopez, Jonathan Brune,  Lizzy O’Connor
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THE STAGES OF EARLY  EMBRYONIC DEVELOPMENT   Epigenesis  proposes that the  form of an embryo gradually  emerged from a formless egg.   Preformation- the belief that  egg or sperm has miniature  embryo  Modern biology has found  that an organism's  development is mostly  determined by the zygote's  genome and the organization  of the egg cell's cytoplasm. http://www.med.unc.edu/embryo_images/ 
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FERTILIZATION Fertilization activates  the egg and brings  together the nuclei of  sperm and  egg  Fertilization is  important because:  It forms a diploid zygote  from the haploid sets of  chromosomes from two  individuals.  It triggers onset of  embryonic  development.  “The image to the [above] shows a mouse  oocyte that has been stained to show  cortical granules (all the small red dots).  In this preparation, genomic DNA in the  metaphase plate of the secondary oocyte  (top right) appears bluish-white.” http://www.vivo.colostate.edu/hbooks/pathphys/
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THE ACROSOMAL REACTION   Upon contacting the egg's jelly coat, the  acrosomal vesicle in the head of the sperm   releases hydrolytic enzymes via exocytosis. These enzymes enable an acrosomal process to  elongate and penetrate the jelly coat. A protein coating the tip of the process  attaches to specific receptors on the egg's  vitelline layer (just external to the plasma  membrane).
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THE ACROSOMAL REACTION   This provides species specificity for  fertilization. The sperm and egg's plasma membranes fuse,  allowing the sperm nucleus to enter  the egg  and causing a depolarization of the plasma  membrane that prevents other  sperm cells  from also uniting with the egg.
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THE CORTICAL REACTION   The fusion of the egg and sperm membranes  stimulates a series of changes in the egg's cortex  known as a cortical reaction The cortical reaction results in the vitelline layer  of the egg to become harden to form the  fertilization membrane. The fertilization membrane prevents entry of  additional sperm. 
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ACTIVATION OF THE EGG   The cortical reaction also  incites metabolic changes  that activates the egg cell.  Cellular respiration and  protein synthesis rates  increase.  The sperm nucleus within the  egg swells and merges with  the egg nucleus to form the  zygote (actual fertilization).  http://www.vivo.colostate.edu/hbooks/path
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GASTRULATION REARRANGES THE  BLASTULA TO FORM A THREE-LAYER  EMBRYO WITH A PRIMITIVE GUT.   Gastrulation: a dramatic rearrangement of the  cells of the blastula   These general cellular mechanisms are 
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CH47Animal Development -...

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