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 Series of progressive changes in an individual from its beginning to maturity Series of progressive changes in an individual from its beginning to maturity Begins when a fertilized egg divides mitotically Begins when a fertilized egg divides mitotically Specialization occurs as a hierarchy of developmental “decisions” Specialization occurs as a hierarchy of developmental “decisions” Development Development

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8-6 Fertilization and Activation Fertilization and Activation A century of research has been conducted on marine invertebrates A century of research has been conducted on marine invertebrates Especially sea urchins Especially sea urchins 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 the vitelline envelope Egg-recognition proteins bind to species-specific sperm receptors on the 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 Prevention of Polyspermy Fertilization cone forms where the sperm contacts the vitelline membrane Fertilization cone forms where the sperm contacts the vitelline membrane Sperm head drawn in and fuses with egg plasma membrane Sperm head drawn in 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 Polyspermy, the entry of more than one sperm Polyspermy, the entry of more than one 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 “fast block” “fast block” Fertilization

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display The cortical reaction follows The cortical reaction follows Fusion of thousands of enzyme-rich cortical granules with the egg membrane Fusion of thousands of enzyme-rich cortical granules with the egg membrane Cortical granules release contents between the membrane and vitelline envelope Cortical granules release contents between the membrane and vitelline envelope Creates an osmotic gradient Creates an osmotic gradient Water rushes into space Water 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 Fertilization

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display One cortical granule enzyme One cortical granule enzyme Causes the vitelline envelope to harden Causes the vitelline envelope to harden Now called the fertilization membrane Now called the fertilization membrane Block to polyspermy is now complete Block to polyspermy is now complete Similar process occurs in mammals Similar process occurs in mammals Fertilization

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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 Enlarged sperm nucleus migrates inward to contact the female nucleus Fusion of male and female nuclei forms a diploid zygote nucleus Fusion of male and female nuclei forms a diploid zygote nucleus Fertilization

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fertilization Fertilization Sets in motion important changes in the egg cytoplasm Sets in motion important changes in the egg cytoplasm Fertilized egg called a zygote Fertilized egg called a zygote 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 Large cytoplasmic mass converted into small maneuverable cells: blastomeres Large cytoplasmic mass converted into small maneuverable cells: blastomeres 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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Egg Types and Cleavage Isolecithal Very little yolk, evenly distibuted Use Holoblastic cleavage- full cleavage Mesolecithal Moderate yolk Use Holoblastic - full cleavage Telolecithal Have an abundance of yolk Use Meroblastic cleavage - partial cleavage

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display An Overview of Development Following Cleavage Blastulation Blastulation Cleavage creates a cluster of cells called the blastula Cleavage creates a cluster of cells called the blastula Blastula stage typically consists of a few hundred to several thousand cells Blastula stage typically consists of a few hundred to several thousand cells During blastula stage, first germ layer forms During blastula stage, first germ layer forms In most animals In most animals Cells are arranged around a fluid-filled cavity called the blastocoel (blas-to-seal) Cells are arranged around a fluid-filled cavity called the blastocoel (blas-to-seal)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Gastrulation and Formation of Two Germ Layers Gastrulation and Formation of Two Germ Layers Gastrulation Gastrulation Results in the formation of a second germ layer Results in the formation of a second germ layer 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 Opening into the cavity: Blastopore 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 Some animals retain the blind gut - the opening does not fully extend to other side (flatworms, sea anemones) Some animals retain the blind gut - the opening does not fully extend to other side (flatworms, sea anemones) Most develop a complete gut - in which the opening extends and produces a second opening, the anus Most develop a complete gut - in which the opening extends and produces a second opening, the anus An Overview of Development Following Cleavage

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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 Triploblastic 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 Epithelial lining of the digestive and respiratory tract, liver, pancreas, Epithelial 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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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Formation of the Coelom (see-lom) Formation of the Coelom (see-lom) Coelom Coelom Body cavity surrounded by mesoderm Body cavity surrounded by mesoderm The method by which the coelom forms is an inherited character The method by which the coelom forms is an inherited character Important in grouping organisms based on developmental characters Important in grouping organisms based on developmental characters Upon completion of coelom formation Upon completion of coelom formation Body has 3 tissue layers and 2 cavities Body has 3 tissue layers and 2 cavities Animals Without a Coelom are called Acoelomates (Ex. flatworms) Animals Without a Coelom are called Acoelomates (Ex. flatworms) An Overview of Development Following Cleavage

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8-32 Developmental Characteristics Two major groups of triploblastic animals (animals with 3 germ layers) Two major groups of triploblastic animals (animals with 3 germ layers) Protostomes and deuterostomes Protostomes and deuterostomes The groups are identified by four developmental characters The groups are identified by four developmental characters Cleavage Patterns (radial or spiral) Cleavage Patterns (radial or spiral) Fate of Blastopore (mouth or anus) Fate of Blastopore (mouth or anus) Coelom Formation (split mesoderm or outpocketing mesoderm) Coelom Formation (split mesoderm or outpocketing mesoderm) Embryo Type (Regulative or Mosaic) Embryo Type (Regulative or Mosaic)

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Fate of Blastopore Fate of Blastopore Deuterostome embryos Deuterostome embryos Develop a complete gut Develop a complete gut Blastopore becomes the anus Blastopore becomes the anus Second opening becomes the mouth Second opening becomes the mouth Protosome embryos Protosome embryos Blastopore becomes the mouth Blastopore becomes the mouth Anus forms from a second opening Anus forms from a second opening Protostomes and Deuterostomes Blastopore Fate Protostomes and Deuterostomes Blastopore Fate

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Enterocoely Enterocoely Mesoderm sides push outward and expand into a pouch-like coelomic compartment Mesoderm sides push outward and expand into a pouch-like coelomic compartment Pouch-like compartment pinches off and forms a mesoderm bound space surrounding the gut Pouch-like compartment pinches off and forms a mesoderm bound space surrounding the gut Occurs in Deuterostomes ( Sea stars, fish, frogs, etc.) Occurs in Deuterostomes ( Sea stars, fish, frogs, etc.) Coelom Formation - mesoderm movement Schizocoely Coelom forms from Coelom forms from Endodermal cells move to blastopore and develop into mesoderm Endodermal cells move to blastopore and develop into mesoderm Mesoderm seperates or splits to form cavity (coelom) Mesoderm seperates or splits to form cavity (coelom) Occurs in Protostome (Earthworms, snails) Occurs in Protostome (Earthworms, snails)

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8-37 Blastula and Gastrula Of Embryos

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Vertebrate Development The Common Vertebrate Heritage The Common Vertebrate Heritage All vertebrate embryos share chordate hallmarks All vertebrate embryos share chordate hallmarks Dorsal neural tube Dorsal neural tube Notochord Notochord Pharyngeal gill pouches with aortic arches Pharyngeal gill pouches with aortic arches Ventral heart Ventral heart Postanal tail Postanal tail

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Amniotes and the Amniotic Egg Amniotes and 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 in which the embryo floats Provides an aqueous environment in which the embryo floats Protection from mechanical shock Protection from mechanical shock Amniotic egg contains 4 extraembryonic membranes including the amnion Amniotic egg contains 4 extraembryonic membranes including the 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 Stores yolk Allantois Allantois Storage of metabolic wastes during development Storage of metabolic wastes during development Respiratory surface for gas exchange Respiratory surface for gas exchange Vertebrate Development

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Chorion Chorion Lies beneath the eggshell Lies beneath the eggshell Encloses the embryo and other extraembryonic membrane Encloses the embryo and other extraembryonic membrane As embryo grows As embryo grows Need for oxygen increases Need for oxygen increases Allantois and chorion fuse to form a respiratory surface, the chorioallantoic membrane Allantois and chorion fuse to form a respiratory surface, the chorioallantoic membrane Vertebrate Development

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display A. Fish Larvae - 1 day old, has large yolk sac B. 10 day old fish larva, developed mouth, yolk sac smaller

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display The Mammalian Placenta and Early Mammalian Development The Mammalian Placenta and Early Mammalian Development Most mammalian embryos do not develop within an egg shell Most mammalian embryos do not develop within an egg shell Develop within the mother’s body Develop within the mother’s body Most retained in the mother’s body Most retained in the mother’s body Monotremes Monotremes Primitive mammals that lay eggs Primitive mammals that lay eggs Large yolky eggs resembling bird eggs Large yolky eggs resembling bird eggs Duck-billed platypus and spiny anteater Duck-billed platypus and spiny anteater Vertebrate Development

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Marsupials Marsupials Embryos born at an early stage of development and Embryos born at an early stage of development and Continue development in abdominal pouch of mother Continue development in abdominal pouch of mother Placental Mammals Placental Mammals Represent 94% of the class Mammalia Represent 94% of the class Mammalia Evolution of the placenta Evolution of the placenta Required reconstruction of extraembryonic membranes Required reconstruction of extraembryonic membranes Modification of oviduct Modification of oviduct Expanded region formed a uterus Expanded region formed a uterus Vertebrate Development

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Early Stages of Mammalian Development (Human) Early Stages of Mammalian Development (Human) Germinal Period (1 st two weeks) Blastocyst transported by oviduct to the uterus Blastocyst transported by oviduct to the uterus Propelled by ciliary action Propelled by ciliary action Around 6 th day Around 6 th day Blastocyst = 100 cells Blastocyst = 100 cells Contacts uterus Contacts uterus By the twelfth day By the twelfth day Implantation is complete Implantation is complete Embryo surrounded by pool of maternal blood Embryo surrounded by pool of maternal blood Chorion thickens, sends out tiny fingerlike projections Chorion thickens, sends out tiny fingerlike projections Chorionic villi Chorionic villi Vertebrate Development

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Amnion Amnion Remains unchanged Remains unchanged Surrounds embryo Surrounds embryo Secretes fluid in which embryo floats Secretes fluid in which embryo floats Yolk sac Yolk sac Contains no yolk Contains no yolk Source of stem cells that give rise to blood and lymphoid cells Source of stem cells that give rise to blood and lymphoid cells Stem cells migrate to into the developing embryo Stem cells migrate to into the developing embryo Vertebrate Development

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Allantois Allantois Not needed to store wastes Not needed to store wastes Contributes to the formation of the umbilical cord Contributes to the formation of the umbilical cord Chorion Chorion Forms most of the placenta Forms most of the placenta Vertebrate Development

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Human embryo showing somites - They will differentiate into skeletal muscle and the axial skeleton