TAILIEUCHUNG - Lecture Biology: Chapter 47 - Niel Campbell, Jane Reece

Chapter 47 - Animal development. In this chapter you will: Describe the acrosomal reaction; describe the cortical reaction; distinguish among meroblastic cleavage and holoblastic cleavage; compare the formation of a blastula and gastrulation in a sea urchin, a frog, and a chick; list and explain the functions of the extraembryonic membranes;. | Chapter 47 Animal Development Overview: A Body-Building Plan It is difficult to imagine that each of us began life as a single cell (fertilized egg) called a zygote. A human embryo at about 6–8 weeks after conception shows development of distinctive features. 1 mm Figure How did this complex embryo form from a single cell? Development is determined by the zygote’s genome and molecules in the egg cytoplasm called Cytoplasmic determinants. Cell differentiation is the specialization of cells in structure and function. Morphogenesis is the process by which an animal takes shape / form. Model organisms are species that are representative of a larger group and easily studied. Classic embryological studies use the sea urchin, frog, chick, and the nematode C. elegans. After fertilization, embryonic development proceeds through cleavage, gastrulation, and organogenesis Important events regulating development occur during fertilization and the three stages that build the animal’s 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 germ layers interact and move to give rise to organs. Fertilization brings the haploid nuclei of sperm and egg together, forming a diploid zygote. The sperm’s contact with the egg’s surface initiates metabolic reactions in the egg that trigger the onset of embryonic development: Acrosomal Reaction Cortical Reaction The Acrosomal Reaction The acrosomal reaction is triggered when the sperm meets the egg. The acrosome at the tip of the sperm 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. Basal body (centriole) Sperm head Sperm-binding receptors Acrosome Jelly coat Vitelline layer Egg plasma membrane Hydrolytic enzymes Acrosomal process Actin filament Sperm nucleus Sperm .

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