8-1 CHAPTER 8 Principles of Development

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8-4 Development Development Begins when a fertilized egg divides mitotically Begins when a fertilized egg divides mitotically Specialization/Division of cells occurs Specialization/Division of cells occurs Cells become specific cell types (ectoderm, endoderm, mesoderm) Cells become specific cell types (ectoderm, endoderm, mesoderm) Development Development

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8-6 Contact and Recognition Between Egg and Sperm Contact and Recognition Between Egg and Sperm Marine organisms Marine organisms release enormous numbers of sperm in the ocean to fertilize eggs release enormous numbers of sperm in the ocean to fertilize eggs Many eggs release a chemical molecule Many eggs release a chemical molecule Attract sperm of the same species Attract sperm of the same species Fertilization

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8-7 Sea urchin sperm Sea urchin sperm Penetrate a jelly layer surrounding egg Penetrate a jelly layer surrounding egg Next, contacts the vitelline envelope Next, contacts the vitelline envelope Thin membrane above the egg plasma membrane Thin membrane above the egg plasma membrane Egg-recognition proteins bind to species-specific sperm receptors on vitelline envelope Egg-recognition proteins bind to species-specific sperm receptors on vitelline envelope Ensures an egg recognizes only sperm of the same species Ensures an egg recognizes only sperm of the same species In the marine environment In the marine environment Many species may be spawning at the same time Many species may be spawning at the same time Similar recognition proteins are found on sperm of vertebrate species Similar recognition proteins are found on sperm of vertebrate species Fertilization

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8-8 Prevention of Polyspermy (entry of more than one sperm) Prevention of Polyspermy (entry of more than one sperm) Sperm head drawn in past vitelline membrane and fuses with egg plasma membrane Sperm head drawn in past vitelline membrane and fuses with egg plasma membrane Important changes in the egg surface block entrance to any additional sperm Important changes in the egg surface block entrance to any additional sperm In the sea urchin, an electrical potential rapidly spreads across the membrane In the sea urchin, an electrical potential rapidly spreads across the membrane Other animals create an osmotic gradient from enzyme reactions Other animals create an osmotic gradient from enzyme reactions Water (osmosis) rushes into space Water (osmosis) rushes into space Elevates the envelope Elevates the envelope Lifts away all bound sperm except the one sperm that has successfully fused with the egg plasma membrane Lifts away all bound sperm except the one sperm that has successfully fused with the egg plasma membrane Known as a cortical reaction Known as a cortical reaction Fertilization

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Binding Sperm to Sea Urchin Egg

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display After sperm and egg membranes fuse Sperm loses its flagellum Sperm loses its flagellum Enlarged sperm nucleus migrates inward to contact the female nucleus - once they meet - fertilized egg is now a ZYGOTE (diploid) Enlarged sperm nucleus migrates inward to contact the female nucleus - once they meet - fertilized egg is now a ZYGOTE (diploid) Zygote now enters cleavage Zygote now enters cleavage Fertilization

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Cleavage and Early Development Cleavage Cleavage Embryo divides repeatedly Embryo divides repeatedly No cell growth occurs, only subdivision until cells reach regular somatic cell size No cell growth occurs, only subdivision until cells reach regular somatic cell size At the end of cleavage At the end of cleavage Zygote has been divided into many hundreds or thousands of cells Zygote has been divided into many hundreds or thousands of cells Blastula is formed Blastula is formed

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cleavage Types Holoblastic Cleavage extends entire length of egg Egg does not contain a lot of yolk, so cleavage occurs throughout egg Example: mammals, sea stars, worms Meroblastic Cells divide sitting on top of yolk Too much yolk and yolk can’t divide Examples: birds, reptiles, fish Both determined by amount of Yolk present

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display An Overview of Development Following Cleavage Blastulation - division of zygote to create a hollow ball of cells Blastulation - division of zygote to create a hollow ball of cells Cluster of cells called the blastula Cluster of cells called the blastula few hundred to several thousand cells few hundred to several thousand cells Forms first germ layer (ectoderm) Forms first germ layer (ectoderm) Cavity called the blastocoel Cavity called the blastocoel

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Gastrulation (Forms 2nd germ layer - endoderm) Gastrulation (Forms 2nd germ layer - endoderm) Involves an invagination of one side of blastula Involves an invagination of one side of blastula Forms a new internal cavity Forms a new internal cavity gastrocoel gastrocoel Opening into the cavity: Blastopore (becomes opening into animal - mouth/anus) Opening into the cavity: Blastopore (becomes opening into animal - mouth/anus) Gastrula has an outer layer of ectoderm and an inner layer of endoderm Gastrula has an outer layer of ectoderm and an inner layer of endoderm An Overview of Development Following Cleavage

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Incomplete/ Blind Gut Complete Gut Generalized Development showing germ layers Blastopore (Opening) Gastrocoel (Cavity)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display The only opening into embryonic gut is the blastopore The only opening into embryonic gut is the blastopore Blind or incomplete gut Blind or incomplete gut Blind gut - the opening does not fully extend to other side (sea anemones) Blind gut - the opening does not fully extend to other side (sea anemones) Complete gut - in which the opening extends and produces a second opening, the anus Complete gut - in which the opening extends and produces a second opening, the anus An Overview of Development Following Cleavage Blind Complete

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Developmental Characteristics Protostomes versus deuterostomes Protostomes versus deuterostomes Fate of Blastopore - opening to gut Fate of Blastopore - opening to gut Deuterostome embryos Deuterostome embryos Blastopore becomes the anus Blastopore becomes the anus Second opening becomes the mouth Second opening becomes the mouth Protostome embryos Protostome embryos Blastopore becomes the mouth Blastopore becomes the mouth Anus forms from a second opening Anus forms from a second opening

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Incomplete/ Blind Gut Complete Gut Generalized Development showing germ layers Blue = Ectoderm Yellow = Endoderm Red = Mesoderm

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Formation of Mesoderm Formation of Mesoderm Animals with two germ layers Animals with two germ layers Diploblastic (Endoderm and Ectoderm) Diploblastic (Endoderm and Ectoderm) Most animals add a 3 rd germ layer Most animals add a 3 rd germ layer Triploblastic (Endoderm, Ectoderm, Mesoderm) Triploblastic (Endoderm, Ectoderm, Mesoderm) Mesoderm Mesoderm 3 rd germ layer 3 rd germ layer Forms between the endoderm and the ectoderm Forms between the endoderm and the ectoderm Mesoderm arises from endoderm Mesoderm arises from endoderm An Overview of Development Following Cleavage

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Germ Layer Outcomes: Ectoderm Ectoderm Epithelium and nervous system Epithelium and nervous system Endoderm Endoderm Lining of the digestive and respiratory tract, liver, pancreas, Lining of the digestive and respiratory tract, liver, pancreas, Mesoderm Mesoderm Muscular system, reproductive system, bone, kidneys, blood Muscular system, reproductive system, bone, kidneys, blood Developmental Characteristics

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8-28 Germ Layer Outcome in mammals

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Formation of the Coelom Formation of the Coelom Coelom Coelom Body cavity surrounded by mesoderm Body cavity surrounded by mesoderm Upon completion of coelom formation Upon completion of coelom formation Body has 3 tissue layers and 2 cavities (coelom and blastocoel) Body has 3 tissue layers and 2 cavities (coelom and blastocoel) Animals Without a Coelom are called Acoelomates (Ex. flatworms) Animals Without a Coelom are called Acoelomates (Ex. flatworms) An Overview of Development Following Cleavage

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Coelom Types Types of organisms based on Coelom Acoelomate - has mesoderm, but not cavity or coelom Pseudocoelomate - has mesoderm, but coelom is NOT completely lined with mesoderm. (Pseudo = False) Coelomates - internal cavity completely lined by mesoderm

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8-32 Blastula and Gastrula Of Embryos

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display The Amniotic Egg The Amniotic Egg Reptiles, birds, and mammals Reptiles, birds, and mammals Embryos develop within the amnion Embryos develop within the amnion Fluid-filled sac that encloses the embryo Fluid-filled sac that encloses the embryo Provides an aqueous environment to protect from mechanical shock Provides an aqueous environment to protect from mechanical shock Amniotic egg contains 4 extraembryonic membranes including the amnion Amniotic egg contains 4 extraembryonic membranes including the amnion Yolk, Chorion, Allantois, Amnion Yolk, Chorion, Allantois, Amnion Vertebrate Development

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display In the shelled amniotic egg: In the shelled amniotic egg: Yolk sac Yolk sac Stores yolk - nutrients Stores yolk - nutrients Allantois Allantois Storage of metabolic wastes during development Storage of metabolic wastes during development Respiratory surface for gas exchange Respiratory surface for gas exchange Helps produce umbilical cord in mammals Helps produce umbilical cord in mammals Chorion Chorion Fuses with allantois to aid in increased respiratory needs Fuses with allantois to aid in increased respiratory needs In mammals will develop into placenta In mammals will develop into placenta Vertebrate Development

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