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Chapter 47: Animal Development. Theories of embryonic development Preformation Belief that egg or sperm contain a miniature embryo/adult form Epigenesis Embryo develops gradually from an egg Developmental plan influenced by Zygote genome Maternal mRNA Cytoplasmic determinants - PowerPoint PPT Presentation
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Chapter 47: Animal Chapter 47: Animal DevelopmentDevelopment
Theories of embryonic developmentTheories of embryonic developmentPreformationPreformation
Belief that egg or sperm contain a miniature Belief that egg or sperm contain a miniature embryo/adult formembryo/adult form
EpigenesisEpigenesisEmbryo develops gradually from an eggEmbryo develops gradually from an eggDevelopmental plan influenced byDevelopmental plan influenced by
Zygote genomeZygote genomeMaternal mRNAMaternal mRNACytoplasmic determinantsCytoplasmic determinants
Cell signaling influences gene expressionCell signaling influences gene expression
FertilizationFertilization Activates the eggActivates the egg brings nuclei of egg & sperm togetherbrings nuclei of egg & sperm together begins begins
embryo metabolic reactionsembryo metabolic reactions Acrosomal ReactionAcrosomal Reaction
Acrosome at sperm tip releases hydrolytic Acrosome at sperm tip releases hydrolytic enzymes which digest egg jelly coat/vitelline enzymes which digest egg jelly coat/vitelline membranemembrane
Ion channels open in egg membraneIon channels open in egg membraneNa+ flows Na+ flows in depolarizing membranein depolarizing membrane prevents other prevents other sperm from fusing with egg (fast block sperm from fusing with egg (fast block polyspermy)polyspermy)
Cortical ReactionCortical Reaction Fusion of egg & sperm stimulates a series of Fusion of egg & sperm stimulates a series of
changes in egg cortexchanges in egg cortex Formation of fertilization envelope to function as Formation of fertilization envelope to function as
a slow-block to polyspermya slow-block to polyspermy
Activation of the eggActivation of the egg Sharp rise in CaSharp rise in Ca2+2+ in egg causes: in egg causes:
Increased cell respiration & protein synthesisIncreased cell respiration & protein synthesis Sperm & egg nuclei to fuseSperm & egg nuclei to fuse DNA replication & first cell division DNA replication & first cell division
90 minutes in sea urchins & frogs90 minutes in sea urchins & frogs 12-36 hours in mammals12-36 hours in mammals
Can be stimulated to occur without spermCan be stimulated to occur without sperm
Fertilization in mammalsFertilization in mammals Fertilization is internal (fallopian tubes)Fertilization is internal (fallopian tubes) Secretions of female tract enhance sperm motilitySecretions of female tract enhance sperm motility Sperm migrates into zona pellucida (3D matrix of Sperm migrates into zona pellucida (3D matrix of
egg)egg) Sperm binds to & depolarizes egg to prevent Sperm binds to & depolarizes egg to prevent
polyspermypolyspermy Diploid nuclei form after 1Diploid nuclei form after 1stst cell division (12-36 hours cell division (12-36 hours
after sperm bind)after sperm bind)
CleavageCleavage Partitions the zygote into smaller cellsPartitions the zygote into smaller cells Rapid succession of mitotic cell divisions without G1 & Rapid succession of mitotic cell divisions without G1 &
G2G2 First 5-7 divisions form cluster of cells= morulaFirst 5-7 divisions form cluster of cells= morula Fluid cavity blastocoel forms in morulaFluid cavity blastocoel forms in morula Hollow ball of cells with fluid within= blastulaHollow ball of cells with fluid within= blastula
Polarity & planesPolarity & planes Vegetal poleVegetal pole
high yolk concentrationhigh yolk concentration forms at posterior end of embryoforms at posterior end of embryo
Animal poleAnimal pole low concentration of yolk low concentration of yolk forms the anterior end of embryoforms the anterior end of embryo
Gray crescentGray crescent near equatornear equator
Types of cleavageTypes of cleavage Meroblastic- incomplete division; found in yolk-rich eggsMeroblastic- incomplete division; found in yolk-rich eggs Holoblastic- complete division; found in eggs with little or Holoblastic- complete division; found in eggs with little or
moderate amounts of yolkmoderate amounts of yolk
GastrulationGastrulation Rearranges the cells in the blastulaRearranges the cells in the blastula
forms a 3 layered embryo with a primitive gut (archenteron)forms a 3 layered embryo with a primitive gut (archenteron) Invagination distributes the cells into layersInvagination distributes the cells into layers
open end of archenteron= blastopore (future anus)open end of archenteron= blastopore (future anus) Germ layersGerm layers
EctodermEctoderm outermost layer outermost layer forms nervous system, skin, hair, nails, eye lensforms nervous system, skin, hair, nails, eye lens
EndodermEndoderm inner layerinner layer gives rise to digestive lining, pancreas, liver, thyroid, lungs, bladdergives rise to digestive lining, pancreas, liver, thyroid, lungs, bladder
MesodermMesoderm middle layermiddle layer gives rise to muscles, skeleton, gonads, excretory & circulatory systemsgives rise to muscles, skeleton, gonads, excretory & circulatory systems
3 layer embryo= gastrula3 layer embryo= gastrulaOrganogenesisOrganogenesis Formation of organs from germ layersFormation of organs from germ layers Localized morphological changes in tissue & cell shapeLocalized morphological changes in tissue & cell shape Neural tube & notochord first to appear & elongate in chordate Neural tube & notochord first to appear & elongate in chordate
embryoembryo Blocks of somites from which vertebrae & muscles will form appear Blocks of somites from which vertebrae & muscles will form appear
along the notochordalong the notochord
AmniotesAmniotes Embryos develop in a fluid-filled sac within a Embryos develop in a fluid-filled sac within a
shell or uterusshell or uterus Formation of extraembryonic membranes (life Formation of extraembryonic membranes (life
support system for embryo); occurs support system for embryo); occurs simultaneously with gastrulationsimultaneously with gastrulation AmnionAmnion
fluid protecting the embryo from temperature & movement fluid protecting the embryo from temperature & movement shocksshocks
ChorionChorion gas exchangegas exchange
AllantoisAllantois gas exchange & metabolic waste storagegas exchange & metabolic waste storage incorporated into umbilical cordincorporated into umbilical cord
Yolk sacYolk sac blood vesselsblood vessels carry food to the embryocarry food to the embryo
Avian developmentAvian development Yolk contains food supplyYolk contains food supply Blastodisc= embryo forming portion of egg Blastodisc= embryo forming portion of egg
on upper surfaceon upper surface Primitive streak- longitudinally thickens along Primitive streak- longitudinally thickens along
blastodiscblastodisc Extraembryonic membranesExtraembryonic membranes
Mammalian developmentMammalian development Fertilization & cleavage occurs in oviductsFertilization & cleavage occurs in oviducts Blastocyst reaches uterus & implants at day 7Blastocyst reaches uterus & implants at day 7 Extra-embryonic membranesExtra-embryonic membranes Organogenesis begins with formation of Organogenesis begins with formation of
neural tube, notochord, & somitesneural tube, notochord, & somites
Morphogenesis Morphogenesis Involves specific changes in cell shape, Involves specific changes in cell shape,
position, & adhesion; reorganization of position, & adhesion; reorganization of the cytoskeletonthe cytoskeleton Morphogenetic movements partially guided Morphogenetic movements partially guided
by extra-cellular matrixby extra-cellular matrix Cell Adhesion Molecules (CAM) contribute to Cell Adhesion Molecules (CAM) contribute to
selective association of cells with one anotherselective association of cells with one another Cytoplasmic determinants help establish Cytoplasmic determinants help establish
body axes & differences among cells of the body axes & differences among cells of the early embryoearly embryo
Inductive signals drive differentiation & Inductive signals drive differentiation & pattern formation in vertebratespattern formation in vertebrates
The “organizer” influences & induces the The “organizer” influences & induces the development of other cellsdevelopment of other cells
Inducers turn some genes on & other offInducers turn some genes on & other off