47_Lecture_Presentation_pt1

47_Lecture_Presentation_pt1 - Chapter 47 Animal Development...

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Unformatted text preview: Chapter 47 Animal Development Overview: A Body-Building Plan Each of us began life as a single cell called a zygote A human embryo at about 68 weeks after conception shows development of distinctive features 1 mm The question of how a zygote becomes an animal has been asked for centuries As recently as the 18th century the prevailing theory was called preformation Idea that the egg or sperm contains a miniature infant, or homunculus , which becomes larger during development Engraving 1694 Development is determined by the zygotes genome and molecules in the egg called cytoplasmic determinants Cell differentiation is the specialization of cells in structure and function Morphogenesis is the process by which an animal takes shape Combination of molecular genetics and classical embryology have led to detailed mechanisms of development into animals with multiple tissues and organs Details differ but many organisms share basic mechanisms and use common genes Model organisms are species that are representative of a larger group and easily studied, for example, Drosophila and Caenorhabditis elegans Classic embryological studies have focused on the sea urchin, frog, chick, and the nematode C. elegans embryonic development proceeds through cleavage, gastrulation, and organogenesis Important events regulating development occur during fertilization and the three stages that build the animals body Cleavage : cell division creates a hollow ball of cells called a blastula Gastrulation : cells are rearranged into a three- layered gastrula Organogenesis : the three layers interact and move to give rise to organs Fertilization Fertilization brings the haploid nuclei of sperm and egg together forming a diploid zygote The sperms contact with the eggs surface initiates metabolic reactions in the egg that trigger the onset of embryonic development Studied extensively in sea urchins The Acrosomal Reaction Triggered when the sperm contacts the jelly coat of the egg The acrosome at the tip of the sperm releases hydrolytic enzymes that digest material surrounding the egg Enables arosomal process to elongate and penetrate coat Molecules at tip of process adhere to receptors extending from egg plasma membrane through surrounding ECM ( vitelline layer ) Ensures egg will be fertilized by sperm of same species Leads to fusion of sperm and egg plasma membrane Sperm nucleus enters egg Ion channels in egg membrane allowing Na + to flow in ( depolarization ) Prevents additional sperm from fusing with egg membrane ( fast block to polyspermy ) Last for only ~1 min The Cortical Reaction...
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47_Lecture_Presentation_pt1 - Chapter 47 Animal Development...

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