Key concepts - SUMMARY OF KEY CONCEPTS Concept 47.1 After fertilization embryonic development proceeds through cleavage gastrulation and

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SUMMARY OF KEY CONCEPTS Concept 47.1  After fertilization, embryonic development proceeds through cleavage,  gastrulation, and organogenesis Add/Edit a Private Note        * Fertilization       Fertilization brings together the nuclei of sperm and egg, forming a diploid zygote,  and activates the egg to initiate the onset of embryonic development. The acrosomal  reaction, which is triggered when the sperm meets the egg, releases hydrolytic enzymes  that digest material surrounding the egg. Gamete contact and/or fusion depolarizes the  egg cell membrane and sets up a fast block to polyspermy in many animals. Sperm-egg  fusion also initiates the cortical reaction, inducing a rise in Ca2+ that stimulates cortical  granules to release their contents outside the egg. This forms a fertilization envelope  that functions as a slow block to polyspermy. In mammalian fertilization, the cortical  reaction modifies the zona pellucida as a slow block to polyspermy. Add/Edit a Private Note        * Cleavage       Fertilization is followed by cleavage, a period of rapid cell division without growth,  which results in the production of a large number of cells called blastomeres. Holoblastic  cleavage, or division of the entire egg, occurs in species whose eggs have little or  moderate amounts of yolk, such as sea urchins, frogs, and mammals. Meroblastic  cleavage, incomplete division of the egg, occurs in species with yolk-rich eggs, such as  birds and other reptiles. Cleavage planes usually follow a specific pattern relative to the 
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This note was uploaded on 04/18/2008 for the course BIOL 1308 taught by Professor Hauser during the Spring '08 term at St. Edwards.

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Key concepts - SUMMARY OF KEY CONCEPTS Concept 47.1 After fertilization embryonic development proceeds through cleavage gastrulation and

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