chapter 43: animal development chapter 43 animal development

Chapter 43: Animal Development

CHAPTER 43Animal Development


Chapter 43: Animal DevelopmentFertilization: Interactions of Sperm and EFertilization: Interactions of Sperm and Egggg

Cleavage: Repackaging the CytoplasmCleavage: Repackaging the Cytoplasm

GastrulationGastrulation: Producing the Body Plan: Producing the Body Plan


Chapter 43: Animal DevelopmentNeurulationNeurulation

: Initiating the Nervous System: Initiating the Nervous System

ExtraembryonicExtraembryonic Membranes Membranes

Human Pregnancy and BirthHuman Pregnancy and Birth


Fertilization: Interactions of Sperm and Egg

• Fertilization involves sperm activation Fertilization involves sperm activation • the acrosomal reactionthe acrosomal reaction• digestion of a path thru outer egg digestion of a path thru outer egg

coveringcovering• species-specific binding of sperm to species-specific binding of sperm to

outer egg coveringouter egg covering• fusion of sperm and egg cell fusion of sperm and egg cell

membranes. membranes. Review Figure 43.1Review Figure 43.1

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Figure 43.1

Figure 43.1Figure 43.1

figure 43-01.jpg


Fertilization: Interactions of Sperm and Egg • Entry of sperm into egg triggers fast Entry of sperm into egg triggers fast

and slow blocks to polyspermy, and in and slow blocks to polyspermy, and in mammals, signals the egg to complete mammals, signals the egg to complete meiosis and begin development. meiosis and begin development.

Review Figures 43.2, 43.3, 43.4Review Figures 43.2, 43.3, 43.4

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Figure 43.2


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Figure 43.3


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Figure 43.4


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Fertilization: Interactions of Sperm and Egg • Sperm and egg contribute Sperm and egg contribute

differentially to the zygote. differentially to the zygote. • The sperm contributes a haploid The sperm contributes a haploid

nucleus and, in some species, a nucleus and, in some species, a centriole. centriole.

• The egg contributes a haploid nucleus, The egg contributes a haploid nucleus, nutrients, ribosomes, mitochondria, nutrients, ribosomes, mitochondria, and informational molecules that will and informational molecules that will control early stages of development.control early stages of development.

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Fertilization: Interactions of Sperm and Egg • The cytoplasmic contents of the egg The cytoplasmic contents of the egg

are not distributed homogeneously, are not distributed homogeneously, and are rearranged after fertilization to and are rearranged after fertilization to set up the major axes of the future set up the major axes of the future embryo. embryo.

Review Figures 43.5, 43.6Review Figures 43.5, 43.6

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Figure 43.5


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Figure 43.6 – Part 1

Figure 43.6 – Part 1Figure 43.6 – Part 1

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figure 43-06b.jpg


Cleavage: Repackaging the Cytoplasm• In most animals, cleavage is a period In most animals, cleavage is a period

of rapid cell division without cell of rapid cell division without cell growth or gene expression. growth or gene expression.

• During cleavage, the cytoplasm of the During cleavage, the cytoplasm of the zygote is repackaged into smaller and zygote is repackaged into smaller and smaller cells.smaller cells.

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Cleavage: Repackaging the Cytoplasm • Cleavage pattern is influenced by Cleavage pattern is influenced by

amount of yolk impeding cleavage amount of yolk impeding cleavage furrow formation and orientation of furrow formation and orientation of mitotic spindles. mitotic spindles.

• The result of cleavage is a mass of The result of cleavage is a mass of cells called a blastula. cells called a blastula.

Review Figure 43.7Review Figure 43.7

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figure 43-07a.jpg




figure 43-07b.jpg


Cleavage: Repackaging the Cytoplasm • Cleavage in mammals is unique in that Cleavage in mammals is unique in that

cell divisions are much slower and cell divisions are much slower and genes are expressed early in the genes are expressed early in the process. process.

• Cleavage results in an inner cell mass Cleavage results in an inner cell mass that becomes the embryo and an outer that becomes the embryo and an outer cell mass that becomes the trophoblast. cell mass that becomes the trophoblast.

• The mammalian embryo at this stage is The mammalian embryo at this stage is called a blastocyst. called a blastocyst.


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Figure 43.8


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Cleavage: Repackaging the Cytoplasm

• Fate maps, which identify what tissues Fate maps, which identify what tissues and organs will form from particular and organs will form from particular blastomeres, can be created for the blastomeres, can be created for the blastula. blastula.


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Figure 43.9


figure 43-09.jpg


Cleavage: Repackaging the Cytoplasm • Some species undergo mosaic Some species undergo mosaic

development: the fate of each cell is development: the fate of each cell is determined by the 8-cell stage. determined by the 8-cell stage.

• Other species undergo regulative Other species undergo regulative development: cells are not determined so development: cells are not determined so early and can change developmental early and can change developmental fates. fates.

• In these species, blastomeres separated In these species, blastomeres separated at early stages can develop into complete at early stages can develop into complete embryos, which are then monozygotic, or embryos, which are then monozygotic, or identical, twins. Review Figure 43.10identical, twins. Review Figure 43.10

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figure 43-10a.jpg




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Gastrulation: Producing the Body Plan• Gastrulation involves massive cell Gastrulation involves massive cell

movements that produce three movements that produce three primary germ layers and place cells primary germ layers and place cells from various regions of the blastula from various regions of the blastula into new associations with one into new associations with one another. another.

Review Table 43.1Review Table 43.1

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Table 43.1

Table 43.1Table 43.1

table 43-01.jpg


Gastrulation: Producing the Body Plan• The initial step of sea urchin and amphibian The initial step of sea urchin and amphibian

gastrulation is inward movement of certain gastrulation is inward movement of certain blastomeres. blastomeres.

• The site of inward movement becomes the The site of inward movement becomes the blastopore.blastopore.

• Cells that move into the blastula become the Cells that move into the blastula become the endoderm and mesoderm; cells remaining on endoderm and mesoderm; cells remaining on the outside become the ectoderm. the outside become the ectoderm.

• Cytoplasmic factors in the vegetal pole cells Cytoplasmic factors in the vegetal pole cells are essential to initiate development. are essential to initiate development.

Review Figure 43.11, 43.12Review Figure 43.11, 43.12

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Figure 43.11


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Figure 43.12


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Gastrulation: Producing the Body Plan• Gastrulation in frogs is initiated when Gastrulation in frogs is initiated when

cells in the gray crescent move into the cells in the gray crescent move into the blastocoel. blastocoel.

• This inward migration creates the This inward migration creates the blastopore.blastopore.

• The dorsal lip of the blastopore is a The dorsal lip of the blastopore is a critical site for the determination of critical site for the determination of tissues. tissues.

• It has been called the primary It has been called the primary embryonic organizer. embryonic organizer.

Review Figures 43.13, 43.14, 43.15Review Figures 43.13, 43.14, 43.153131




figure 43-13a.jpg




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Figure 43.14


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figure 43-15b.jpg


Gastrulation: Producing the Body Plan• The anterior–posterior axis of the frog The anterior–posterior axis of the frog

blastula appears to be determined by blastula appears to be determined by the distribution of the protein the distribution of the protein -catenin -catenin

• This activates a signaling cascade that This activates a signaling cascade that induces the primary embryonic induces the primary embryonic organizer.organizer.

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Gastrulation: Producing the Body Plan

• Gastrulation in reptiles and birds Gastrulation in reptiles and birds differs from that in sea urchins and differs from that in sea urchins and frogs because the large egg yolk frogs because the large egg yolk causes the blastula to form a flattened causes the blastula to form a flattened disc of cells. disc of cells.


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figure 43-16a.jpg




figure 43-16b.jpg


Gastrulation: Producing the Body Plan• Mammals have a pattern of Mammals have a pattern of

gastrulation similar to that of birds, gastrulation similar to that of birds, even though they have no yolk. even though they have no yolk.


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Figure 43.17


figure 43-17.jpg


Neurulation: Initiating the Nervous System• Neurulation follows gastrulation. Neurulation follows gastrulation. • Cells that migrate over the dorsal lip of the Cells that migrate over the dorsal lip of the

blastopore are determined to be blastopore are determined to be chordomesoderm, which forms the notochord. chordomesoderm, which forms the notochord.

• The notochord induces the overlying ectoderm The notochord induces the overlying ectoderm to thicken, form parallel ridges, and fold in on to thicken, form parallel ridges, and fold in on itself to form a neural tube below the itself to form a neural tube below the epidermal ectoderm. epidermal ectoderm.

• The nervous system develops from the neural The nervous system develops from the neural tube. tube.


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Figure 43.18 – Part 1Figure 43.18 – Part 1Figure 43.18 – Part 1

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Neurulation: Initiating the Nervous System • The notochord and neural crest cells The notochord and neural crest cells

participate in the segmental participate in the segmental organization of tissues called somites organization of tissues called somites along the body axis. along the body axis.

• Rudimentary organs and organ Rudimentary organs and organ systems form during this stage. systems form during this stage.


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Figure 43.19


figure 43-19.jpg


Neurulation: Initiating the Nervous System • Four families of Hox genes determine Four families of Hox genes determine

anterior–posterior pattern anterior–posterior pattern differentiation along the body axis in differentiation along the body axis in mammals. mammals.

• Other genes such as Other genes such as sonic hedgehogsonic hedgehog, , contribute to dorsal–ventral contribute to dorsal–ventral differentiation. differentiation.


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figure 43-20a.jpg




figure 43-20b.jpg


Extraembryonic Membranes• The embryos of reptiles, birds, and mammals The embryos of reptiles, birds, and mammals

are protected and nurtured by four are protected and nurtured by four extraembryonic membranes. extraembryonic membranes.

• In birds and reptiles the yolk sac surrounding In birds and reptiles the yolk sac surrounding the yolk provides nutrients to the embryothe yolk provides nutrients to the embryo

• The chorion lines the eggshell and The chorion lines the eggshell and participates in gas exchangeparticipates in gas exchange

• The amnion surrounds the embryo enclosing The amnion surrounds the embryo enclosing it in an aqueous environmentit in an aqueous environment

• The allantois stores metabolic wastes. The allantois stores metabolic wastes.


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Figure 43.21


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Extraembryonic Membranes • In mammals, the chorion and the In mammals, the chorion and the

trophoblast cells interact with the trophoblast cells interact with the maternal uterus to form a placenta, for maternal uterus to form a placenta, for nutrient and gas exchange. nutrient and gas exchange.

• The amnion encloses the embryo in an The amnion encloses the embryo in an aqueous environment. aqueous environment.


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Figure 43.22


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Extraembryonic Membranes • Samples of amniotic fluid or pieces of Samples of amniotic fluid or pieces of

chorion can be taken during pregnancy chorion can be taken during pregnancy and analyzed for evidence of genetic and analyzed for evidence of genetic disease. disease.


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Figure 43.23


figure 43-23.jpg


Human Pregnancy and Birth• Pregnancy in humans can be divided Pregnancy in humans can be divided

into three trimesters. into three trimesters. • Early embryogenesis occurs in the first Early embryogenesis occurs in the first

trimester; during this time, the embryo trimester; during this time, the embryo is vulnerable to damage that could lead is vulnerable to damage that could lead to birth defects. to birth defects.

• Hormonal changes, including high hCG, Hormonal changes, including high hCG, estrogen, and progesterone levels, estrogen, and progesterone levels, block further ovulation and block further ovulation and menstruation and cause symptoms of menstruation and cause symptoms of pregnancy.pregnancy.

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Human Pregnancy and Birth • During the second and third trimesters During the second and third trimesters

the embryo grows, the limbs elongate, the embryo grows, the limbs elongate, and organ systems mature.and organ systems mature.

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Human Pregnancy and Birth • The onset of labor is due to many The onset of labor is due to many

hormonal and mechanical factors, hormonal and mechanical factors, which increase contractility of uterine which increase contractility of uterine muscles. Oxytocin plays a major role in muscles. Oxytocin plays a major role in a positive feedback loop. a positive feedback loop.


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Figure 43.25


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Human Pregnancy and Birth • Birth is not the end of development, Birth is not the end of development,

which continues throughout childhood which continues throughout childhood and throughout life. and throughout life.

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chapter 43: animal development chapter 43 animal development

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