Chapter 43: Animal Development CHAPTER 43 Animal Development

Chapter 43: Animal Development Fertilization: Interactions of Sperm and Egg Fertilization: Interactions of Sperm and Egg Cleavage: Repackaging the Cytoplasm Cleavage: Repackaging the Cytoplasm Gastrulation: Producing the Body Plan Gastrulation: Producing the Body Plan

Chapter 43: Animal Development Neurulation: Initiating the Nervous System Neurulation: Initiating the Nervous System Extraembryonic Membranes Extraembryonic Membranes Human Pregnancy and Birth Human Pregnancy and Birth

Chapter 43: Animal Development Fertilization: Interactions of Sperm and Egg Fertilization involves sperm activationFertilization involves sperm activation the acrosomal reactionthe acrosomal reaction digestion of a path thru outer egg coveringdigestion of a path thru outer egg covering species-specific binding of sperm to outer egg coveringspecies-specific binding of sperm to outer egg covering fusion of sperm and egg cell membranes. Review Figure 43.1fusion of sperm and egg cell membranes. Review Figure

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Chapter 43: Animal Development Fertilization: Interactions of Sperm and Egg Entry of sperm into egg triggers fast and slow blocks to polyspermy, and in mammals, signals the egg to complete meiosis and begin development.Entry of sperm into egg triggers fast and slow blocks to polyspermy, and in mammals, signals the egg to complete meiosis and begin development. Review Figures 43.2, 43.3,

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Chapter 43: Animal Development Fertilization: Interactions of Sperm and Egg Sperm and egg contribute differentially to the zygote.Sperm and egg contribute differentially to the zygote. The sperm contributes a haploid nucleus and, in some species, a centriole.The sperm contributes a haploid nucleus and, in some species, a centriole. The egg contributes a haploid nucleus, nutrients, ribosomes, mitochondria, and informational molecules that will control early stages of development.The egg contributes a haploid nucleus, nutrients, ribosomes, mitochondria, and informational molecules that will control early stages of development.10

Chapter 43: Animal Development Fertilization: Interactions of Sperm and Egg The cytoplasmic contents of the egg are not distributed homogeneously, and are rearranged after fertilization to set up the major axes of the future embryo.The cytoplasmic contents of the egg are not distributed homogeneously, and are rearranged after fertilization to set up the major axes of the future embryo. Review Figures 43.5,

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Chapter 43: Animal Development Cleavage: Repackaging the Cytoplasm In most animals, cleavage is a period of rapid cell division without cell growth or gene expression.In most animals, cleavage is a period of rapid cell division without cell growth or gene expression. During cleavage, the cytoplasm of the zygote is repackaged into smaller and smaller cells.During cleavage, the cytoplasm of the zygote is repackaged into smaller and smaller cells.15

Chapter 43: Animal Development Cleavage: Repackaging the Cytoplasm Cleavage pattern is influenced by amount of yolk impeding cleavage furrow formation and orientation of mitotic spindles.Cleavage pattern is influenced by amount of yolk impeding cleavage furrow formation and orientation of mitotic spindles. The result of cleavage is a mass of cells called a blastula.The result of cleavage is a mass of cells called a blastula. Review Figure

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Chapter 43: Animal Development Cleavage: Repackaging the Cytoplasm Cleavage in mammals is unique in that cell divisions are much slower and genes are expressed early in the process.Cleavage in mammals is unique in that cell divisions are much slower and genes are expressed early in the process. Cleavage results in an inner cell mass that becomes the embryo and an outer cell mass that becomes the trophoblast.Cleavage results in an inner cell mass that becomes the embryo and an outer cell mass that becomes the trophoblast. The mammalian embryo at this stage is called a blastocyst.The mammalian embryo at this stage is called a blastocyst. Review Figure

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Chapter 43: Animal Development Cleavage: Repackaging the Cytoplasm Fate maps, which identify what tissues and organs will form from particular blastomeres, can be created for the blastula.Fate maps, which identify what tissues and organs will form from particular blastomeres, can be created for the blastula. Review Figure

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Chapter 43: Animal Development Cleavage: Repackaging the Cytoplasm Some species undergo mosaic development: the fate of each cell is determined by the 8- cell stage.Some species undergo mosaic development: the fate of each cell is determined by the 8- cell stage. Other species undergo regulative development: cells are not determined so early and can change developmental fates.Other species undergo regulative development: cells are not determined so early and can change developmental fates. In these species, blastomeres separated at early stages can develop into complete embryos, which are then monozygotic, or identical, twins. Review Figure 43.10In these species, blastomeres separated at early stages can develop into complete embryos, which are then monozygotic, or identical, twins. Review Figure

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Chapter 43: Animal Development Gastrulation: Producing the Body Plan Gastrulation involves massive cell movements that produce three primary germ layers and place cells from various regions of the blastula into new associations with one another.Gastrulation involves massive cell movements that produce three primary germ layers and place cells from various regions of the blastula into new associations with one another. Review Table

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Chapter 43: Animal Development Gastrulation: Producing the Body Plan The initial step of sea urchin and amphibian gastrulation is inward movement of certain blastomeres.The initial step of sea urchin and amphibian gastrulation is inward movement of certain blastomeres. The site of inward movement becomes the blastopore.The site of inward movement becomes the blastopore. Cells that move into the blastula become the endoderm and mesoderm; cells remaining on the outside become the ectoderm.Cells that move into the blastula become the endoderm and mesoderm; cells remaining on the outside become the ectoderm. Cytoplasmic factors in the vegetal pole cells are essential to initiate development.Cytoplasmic factors in the vegetal pole cells are essential to initiate development. Review Figure 43.11, Review Figure 43.11,

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Chapter 43: Animal Development Gastrulation: Producing the Body Plan Gastrulation in frogs is initiated when cells in the gray crescent move into the blastocoel.Gastrulation in frogs is initiated when cells in the gray crescent move into the blastocoel. This inward migration creates the blastopore.This inward migration creates the blastopore. The dorsal lip of the blastopore is a critical site for the determination of tissues.The dorsal lip of the blastopore is a critical site for the determination of tissues. It has been called the primary embryonic organizer.It has been called the primary embryonic organizer. Review Figures 43.13, 43.14,

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Chapter 43: Animal Development Gastrulation: Producing the Body Plan The anterior–posterior axis of the frog blastula appears to be determined by the distribution of the protein  -cateninThe anterior–posterior axis of the frog blastula appears to be determined by the distribution of the protein  -catenin This activates a signaling cascade that induces the primary embryonic organizer.This activates a signaling cascade that induces the primary embryonic organizer.37

Chapter 43: Animal Development Gastrulation: Producing the Body Plan Gastrulation in reptiles and birds differs from that in sea urchins and frogs because the large egg yolk causes the blastula to form a flattened disc of cells.Gastrulation in reptiles and birds differs from that in sea urchins and frogs because the large egg yolk causes the blastula to form a flattened disc of cells. Review Figure

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Chapter 43: Animal Development Gastrulation: Producing the Body Plan Mammals have a pattern of gastrulation similar to that of birds, even though they have no yolk.Mammals have a pattern of gastrulation similar to that of birds, even though they have no yolk. Review Figure

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Chapter 43: Animal Development Neurulation: Initiating the Nervous System Neurulation follows gastrulation.Neurulation follows gastrulation. Cells that migrate over the dorsal lip of the blastopore are determined to be chordomesoderm, which forms the notochord.Cells that migrate over the dorsal lip of the blastopore are determined to be chordomesoderm, which forms the notochord. The notochord induces the overlying ectoderm to thicken, form parallel ridges, and fold in on itself to form a neural tube below the epidermal ectoderm.The notochord induces the overlying ectoderm to thicken, form parallel ridges, and fold in on itself to form a neural tube below the epidermal ectoderm. The nervous system develops from the neural tube.The nervous system develops from the neural tube. Review Figure

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Chapter 43: Animal Development Neurulation: Initiating the Nervous System The notochord and neural crest cells participate in the segmental organization of tissues called somites along the body axis.The notochord and neural crest cells participate in the segmental organization of tissues called somites along the body axis. Rudimentary organs and organ systems form during this stage.Rudimentary organs and organ systems form during this stage. Review Figure

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Chapter 43: Animal Development Neurulation: Initiating the Nervous System Four families of Hox genes determine anterior–posterior pattern differentiation along the body axis in mammals.Four families of Hox genes determine anterior–posterior pattern differentiation along the body axis in mammals. Other genes such as sonic hedgehog, contribute to dorsal–ventral differentiation.Other genes such as sonic hedgehog, contribute to dorsal–ventral differentiation. Review Figure

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Chapter 43: Animal Development Extraembryonic Membranes The embryos of reptiles, birds, and mammals are protected and nurtured by four extraembryonic membranes.The embryos of reptiles, birds, and mammals are protected and nurtured by four extraembryonic membranes. In birds and reptiles the yolk sac surrounding the yolk provides nutrients to the embryoIn birds and reptiles the yolk sac surrounding the yolk provides nutrients to the embryo The chorion lines the eggshell and participates in gas exchangeThe chorion lines the eggshell and participates in gas exchange The amnion surrounds the embryo enclosing it in an aqueous environmentThe amnion surrounds the embryo enclosing it in an aqueous environment The allantois stores metabolic wastes.The allantois stores metabolic wastes. Review Figure

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Chapter 43: Animal Development Extraembryonic Membranes In mammals, the chorion and the trophoblast cells interact with the maternal uterus to form a placenta, for nutrient and gas exchange.In mammals, the chorion and the trophoblast cells interact with the maternal uterus to form a placenta, for nutrient and gas exchange. The amnion encloses the embryo in an aqueous environment.The amnion encloses the embryo in an aqueous environment. Review Figure

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Chapter 43: Animal Development Extraembryonic Membranes Samples of amniotic fluid or pieces of chorion can be taken during pregnancy and analyzed for evidence of genetic disease.Samples of amniotic fluid or pieces of chorion can be taken during pregnancy and analyzed for evidence of genetic disease. Review Figure

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Chapter 43: Animal Development Human Pregnancy and Birth Pregnancy in humans can be divided into three trimesters.Pregnancy in humans can be divided into three trimesters. Early embryogenesis occurs in the first trimester; during this time, the embryo is vulnerable to damage that could lead to birth defects.Early embryogenesis occurs in the first trimester; during this time, the embryo is vulnerable to damage that could lead to birth defects. Hormonal changes, including high hCG, estrogen, and progesterone levels, block further ovulation and menstruation and cause symptoms of pregnancy.Hormonal changes, including high hCG, estrogen, and progesterone levels, block further ovulation and menstruation and cause symptoms of pregnancy.58

Chapter 43: Animal Development Human Pregnancy and Birth During the second and third trimesters the embryo grows, the limbs elongate, and organ systems mature.During the second and third trimesters the embryo grows, the limbs elongate, and organ systems mature.59

Chapter 43: Animal Development Human Pregnancy and Birth The onset of labor is due to many hormonal and mechanical factors, which increase contractility of uterine muscles. Oxytocin plays a major role in a positive feedback loop.The onset of labor is due to many hormonal and mechanical factors, which increase contractility of uterine muscles. Oxytocin plays a major role in a positive feedback loop. Review Figure

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Chapter 43: Animal Development Human Pregnancy and Birth Birth is not the end of development, which continues throughout childhood and throughout life.Birth is not the end of development, which continues throughout childhood and throughout life.62