Animal Animal DevelepmentDevelepment

Chapter 53Chapter 53

Sila and KhareeSila and Kharee

Fertilization Fertilization Fertilization, the union of male and female Fertilization, the union of male and female

gametes, is the first step in reproduction.gametes, is the first step in reproduction. Sperm must penetrate to the plasma Sperm must penetrate to the plasma

membranemembrane Saclike organelle named the acrosome is Saclike organelle named the acrosome is

positioned between the plasma membrane positioned between the plasma membrane and nucleus of sperm, digestive enzymes and nucleus of sperm, digestive enzymes within create a hole in eggs membranewithin create a hole in eggs membrane

The egg is protected by coatsThe egg is protected by coats zona pellucide (mammals)zona pellucide (mammals) Jelly layer (urchin, frogs)Jelly layer (urchin, frogs) Chorion (insects)Chorion (insects)

Membrane Fusion Activates Membrane Fusion Activates the Eggthe Egg

The egg remain dormant until the sperm The egg remain dormant until the sperm activates itactivates it

Polyspermy: response to sperm fusion of Polyspermy: response to sperm fusion of additional spermadditional sperm

Sperm penetration of egg can also cause:Sperm penetration of egg can also cause: Many eggs did not complete meiosis, therefore Many eggs did not complete meiosis, therefore

not a haploid yet, sperm penetration activatesnot a haploid yet, sperm penetration activates Triggers movement of egg cytoplasmTriggers movement of egg cytoplasm Sharp increase of protein synthesis and Sharp increase of protein synthesis and

metabolic activity in generalmetabolic activity in general

The Fusion of NucleiThe Fusion of Nuclei

Final Stage of FertilizationFinal Stage of Fertilization The haploid male nuclei and the The haploid male nuclei and the

haploid female form the diploid haploid female form the diploid zygotezygote

Two nuclei migrate toward each Two nuclei migrate toward each other along a asterother along a aster

Clevage and Blastula Clevage and Blastula StageStage

Cleavage: The rapid division of the Cleavage: The rapid division of the zygote into a larger and larger zygote into a larger and larger number of smaller cells.number of smaller cells.

Blastomere: Each individual cellBlastomere: Each individual cell Animal Pole and Vegetal PoleAnimal Pole and Vegetal Pole

BlastulaBlastula

The blastula is a hollow mass of cellsThe blastula is a hollow mass of cells Outermost blastomeres join together Outermost blastomeres join together

through protein belt which create a through protein belt which create a seal that isolates the interior cell seal that isolates the interior cell massmass

Cleavage patterns are diverse in Cleavage patterns are diverse in every animal cellevery animal cell

Cleavage PatternsCleavage Patterns

Eggs with moderate or little yolk go Eggs with moderate or little yolk go through Hoboblastic Cleavage through Hoboblastic Cleavage (Complete)(Complete) EchinodermsEchinoderms Annelids, Mollusks, and FlatwormsAnnelids, Mollusks, and Flatworms

Eggs with Dense Yolk go through Eggs with Dense Yolk go through Meroblastic Cleavage (incomplete)Meroblastic Cleavage (incomplete) Fish, Reptiles, BirdsFish, Reptiles, Birds InsectsInsects

Cleavage in MammalsCleavage in Mammals

Contain little yolkContain little yolk Holoblastic, forms a structure called a Holoblastic, forms a structure called a

blastocystblastocyst A single layer of cells surrounds a A single layer of cells surrounds a

blastocoelblastocoel Inner cell mass (ICM) located at one pole Inner cell mass (ICM) located at one pole

of of blastocoelof of blastocoel Trophoblast, the outer cells, part of them Trophoblast, the outer cells, part of them

enter the maternal uterus lining and forms enter the maternal uterus lining and forms placentaplacenta

GastrulationGastrulation

Gastrulation: Cells of blastula Gastrulation: Cells of blastula rearrange themselves to form the rearrange themselves to form the body planbody plan

Forms the three germ bilayersForms the three germ bilayers Converts the blastula into a Converts the blastula into a

bilaterally symmetrical embryo with bilaterally symmetrical embryo with a gut, visible anterior and posterior, a gut, visible anterior and posterior, and dorsal ventral axis.and dorsal ventral axis.

How the Cells MoveHow the Cells Move

Lamellipdoa: crawl over neighbor Lamellipdoa: crawl over neighbor cellscells

Filopodia: feel out the surfaces of Filopodia: feel out the surfaces of other cells and pull the cell forwardother cells and pull the cell forward

Tightly attached cells move in sheetsTightly attached cells move in sheets

Gastrulation in Gastrulation in ChordatesChordates

The movement of surface cells into The movement of surface cells into the interior, the interior, by folding as a sheet by folding as a sheet ("("invaginationinvagination“)“)

The cells of vegetal plate move The cells of vegetal plate move inward to the blastocoel cavityinward to the blastocoel cavity

The cells produce a tube (primitive The cells produce a tube (primitive gut) called archenteron and the gut) called archenteron and the opening (anus)opening (anus)

Gastrulation in Gastrulation in AmphibiansAmphibians

By rolling as a sheet ("By rolling as a sheet ("involutioninvolution")") Cells from animal pole move to Cells from animal pole move to

vegetal polevegetal pole When on the dorsal lip, cells involute When on the dorsal lip, cells involute

into interior into interior Movement of the cells forms a new Movement of the cells forms a new

internal cavityinternal cavity Organogenesis then begins (explained Organogenesis then begins (explained

later)later)

Amphibian GastrulationAmphibian Gastrulation

Gastrulation in Gastrulation in Reptiles /Birds/ and Reptiles /Birds/ and

MammalsMammals The Gastrulation of all are similar by The Gastrulation of all are similar by

internalization/separation of cells internalization/separation of cells from an epithelium ("from an epithelium ("ingressioningression "), "),

The embryo develops from flattened The embryo develops from flattened collection of cells forming two layers collection of cells forming two layers (endoderm and ectoderm) lower (endoderm and ectoderm) lower cells migrate out to line cavity to cells migrate out to line cavity to form yolk (ectoderm) mesoderm form yolk (ectoderm) mesoderm cells migrate to the interiorcells migrate to the interior

Three Germ LayersThree Germ Layers Endoderm: formed by cells that move into Endoderm: formed by cells that move into

embryo to form the tube of a primitive gutembryo to form the tube of a primitive gut Epidermis of skin, nervous system, sense organsEpidermis of skin, nervous system, sense organs

Ectoderm: formed by the cells that remain Ectoderm: formed by the cells that remain on the exterioron the exterior

Skeleton, muscles, blood vessels, heart, blood, Skeleton, muscles, blood vessels, heart, blood, gonads, kidneys, dermis of skingonads, kidneys, dermis of skin

Mesoderm: formed by the cells that move Mesoderm: formed by the cells that move into the space between endoderm and into the space between endoderm and ectodermectoderm

Lining of digestive and respiratory tracts, liver, Lining of digestive and respiratory tracts, liver, pancreas, thymus, thyroidpancreas, thymus, thyroid