co44 - CHAPTER 44 DEVELOPMENT Chapter Outline 44.1 Early...

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CHAPTER 44 D EVELOPMENT Chapter Outline 44.1 Early Developmental Stages A. Fertilization 1. Fertilization requires that sperm and egg interact to form a zygote . a. A sperm has three parts. 1) The head contains a haploid nucleus covered by a caplike acrosome containing enzymes allowing the sperm to penetrate the egg. 2) A middle piece contains ATP-producing mitochondria. 3) The tail is a flagellum that allows the sperm to swim. 2. The plasma membrane of the egg is surrounded by the zona pellucida. a. The zona pellucida is surrounded by a few layers of adhering follicular cells, collectively called the corona radiata. b. These cells nourished the egg when it was in a follicle of the ovary. 3. Fertilization involves the following steps which are species-specific. a. Several sperm penetrate the corona radiata and several sperm attempt to penetrate the zona pellucida. b. One sperm enters the egg and their nuclei eventually fuse. c. After the sperm head binds tightly to the zona pellucida, the acrosome enzymes digest form a pathway for the sperm through the zona pellucida. d. Th head, middle piece and usually the tail enters the egg. e. Prevention of polyspermy depends on changes in the egg plasma membrane when the sperm touches the egg and depolarizes the egg plasma membrane. f. As soon as plasma membranes of the sperm and egg fuse, the zona pellucida lifts away from the surface of the egg, forming a moat that prevents entrance of any other sperm. g. Vitelline envelope is now fertilization envelope. B. Embryonic Development 1. Development is all of the changes that occur during the life cycle of an organism. 2. An organism is an embryo during the first stages of development. 3. Most animals go through the same embryonic stages: zygote, morula, blastula, early and late gastrula. 4. After fertilization, a zygote undergoes cleavage , cell division without growth. 5. DNA replication and mitosis occur repeatedly; and the cells get smaller each division. 6. In the lancelet, the cell divisions are equal in the resulting morula . 7. A cavity called the blastocoel develops forming a hollow ball called the blastula . 8. Gastrulation is the invagination of some cells into the blastocoel to form the two of the three primary germ layers . a. The outer layer of cells becomes ectoderm ; ectoderm gives rise to the epidermis of the skin, the epithelial lining of the mouth and rectum, and the nervous system. b. The inner layer of cells becomes the endoderm that gives rise to the epithelial lining of the digestive tract and the respiratory tract, associated glands of the digestive and respiratory system, and the lining of urinary bladder. c. The middle mesoderm begins as an outpocketing of the primitive gut. 1)
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This note was uploaded on 10/24/2009 for the course BIO 172 taught by Professor Clark during the Fall '08 term at University of Michigan.

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co44 - CHAPTER 44 DEVELOPMENT Chapter Outline 44.1 Early...

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