development of amphioxus
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The Embryology Of The Amphioxus
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Origins of Sex Cells
Section in a vertebrate
embryo showing the origin
of primordial germ cells. Stages of sexualdifferentiation
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Types of eggs according the yolk distribution
Isolecithal (homolecithal)
Amphioxus
Telolecithal (Mesolecithal)
Frog
yolk
Telolecithal ( Macrolecithal, Megalecithal) Centrolecithal
Bony fish, reptiles, birds oviparous mammals Insects , Arthropods
yolk
yolk
Yolk
Germinal disc
( , 1 - , 12mm diameter) (1.216 mm diameter)
ChickBony fishs Insect egg
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1 - Cleavage 2 blastulation 3 gastrulation 4
Organogesis
1 - Cleavage
Types of cleavage Plane of cleavage
Micromere
Macromere
Meroblastic,
discoidal, partial
(chick)
Holoblastic,
equal
(Amphioxus)
Holoblastic,
Unequal
(Frog)
2- blastomere 4 - blastomere
Latitudinal
Meridional
Holoblastic, equal(Mammal)
Blastoderm
yolk
Stages of the embryonic development
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Amphioxus
Fish
Sturgeon)
Amphibia
Frog)
Reptilia
Turtle)
Bird
Chick)
Mammal
Man)
Shape of Sperms in Vertebrate Animal
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Gene expression and protein synthesis
During development
-Cell behavior provides the link between
gene actionand developmental processes.-Genes control behavior by controlling which
proteinsare made by a cell.-Differential gene activity control
development.
- Development is progressive and the fate ofcells becomes determined at different times.
- As embryonic development proceeds the
organization complexity of the embryo
becomes vastly increased over that of the
fertilized egg.
- Differentialk gene activity controlsdevelopment.
- Inductive interactions can make cells
different from each cells.
- The response to inductive signalsdepends on
the state of the cell.
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An inducing signal can be transmitted from one cell to
another in three main ways
1
DiffusionThe signal can be a diffusible
molecule, which interacts with a
receptor on the target cell surface.
2- Direct contact
The signal can be produced by
direct contact between two
complementary proteins at the cell
surfaces.
3
Gap junctionIf the signal involves smallmolecules it may pass directly from cell
to cell through gap junctions in the
plasma membrane.
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Return chromosome number to
diploid value
Activation of development
Basic steps:Sperm activation/capacitation
Attraction of sperm to egg
Binding/passing through egg envelopeFusion of plasma membranes
Egg Activation
Fertilization
- Fertilization cone:
-Fusogenic
proteins
Bindin
Fertilin
- Nucleus,mitochondria, and
centriole all enter
the egg
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FertilizationScanning electron micrograph of an egg
after the attraction of sperms.
Egg
Sperm
Sperm
Egg
Sperm
SEM showing the sperm
incorporation into egg.
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Hypothetical pathway for calcium release
IP3 Inositol triphosphate
Dag diacylglycerol
PIP3 phosphatdidylinositol Triphosphate
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Introduction
Embryologydeals with the development of the individual
from the fertilized egg or, in rare instances, from the unfertilized egg
to a stage resembling more or less closely the adult form.
Ontogeny is a broader and more comprehensive term thatincludes both the embryonic period and the entire postembryonicdevelopment of the individual to its adult condition.
In a general sense, ontogeny is the history of development of an
organism from the fertilized egg to sexual maturity.
Butterflies eggs Larvae (caterpillars) Pupa casesmetamorphosis
Butterflies
Marsupial mammals
(Kangaroo or opossum)
Immature embryo Postnatal in marsupial pouch
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Reproduction
Multicellular animals
(Metazoa)
Sexual reproduction(syngamy)
Asexual reproduction(agamy)
Ex. Budding (Hydra)
Strobilization (Aurelia)
Constriction (annelid)
The new individual is produced not by
somatic cells of the parent but by sex
cells, or gametes (sperm from male andovum from femal) which differ essentially
from somatic cells in having undergone
meiosis a process in which the number of
chromosomes is reduced to one-half of
the diploid (2n) number found in somatic
cells. Furthermore, the sex cells are
generally capable of developing into a
new individual only after two have united
in a process called fertilization.
( eggs develop without fertilization)
invertebrate animals (honeybee)
Produced from fertilized eggs
drones Produced from unfertlized eggs
The new individual is derived from a
blastem ( a group of cells from the
parent body)
Chromosomes of the blastema is the
same as in the other somatic cells ofthe parent (diploid set) 2n.
Workers and Queens
Daphnia
honeybee
Parthenogenesis
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O
vu
Spermatogenesis
Oogenesis
Both include:
Reduction in
chromosome number
by meiosis
Acquisition of
structural and
functional characters
Gametogenesis
Ootid
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Mitosis Review
ProphaseInterphase
AnaphaseMetaphase
Telophase
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Prophase I
Leptotema
Zygonema
Pachynema**
Diplonema**
Diakenesis
Meiosis Review
Meiosis I
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Anaphase I and Telophase I
Metaphase
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Meiosis II
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The ovulation in human
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Types of stem cells1-Embryonic stem cells (ES cells)Totipotent stem cells Only the morula s cells are totipotent, able to
become all tissues and a placenta
-Pluripotent stem cells, originate as inner cells within a blastocyst and
they can become any tissue in the body, excluding a placenta.-Human embryos reach the blastocyst stage 4-5 days post fertilization,at which time they consist of 50-150 cells.
-They are able to differentiate into all derivatives of the three primary
germ layers: ectoderm, endoderm, and mesoderm.
-Multipotent stem cells Stem cells can produce only cells of a closely
related family of cells (e.g. hematopoitic stem cells differentiate intored blood cells, while blood cells, platelets. Etc.).
-2-Adult stem cells
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Eggs of amphioxus are released by rupture of follicular membranes and overlyingtissues so that then find their way first into the atrium and then via the atriopore
into the sea. By this time the first polar body has been separated off and comesto lie just outside the thin vitelline membrane.
The egg of Amphioxus
Second
polar
body
First polar bodyNucleolus
Nucleus
Yolk
Unfertilized egg Fertilized egg
AcrosomeHeadTail
Cenriole
The sperm of Amphioxus
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Fertilization inAmphioxus
After the entry of the sperm into the
egg cytoplasm the egg nucleus
completes its maturation division and
the second polar body is extruded.
Scheme of maturation, syngamy,
karyogamy of the ovum.
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polar bodies
Polar body
2
Blastomere stage
Cleavage
( 2 blastomere stage)
Holoblastic division
Plane is latitudinal
First cleavage
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4 and 8 blastomere stage
Plane of
division is
latitudinal
Plane ofdivision is
latitudinal
(vertical)
Vertical at right angle to the
first two and passes through
just above the equater
Micromere
Macromere
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Blastulation in Amphioxus
T.S of the blastulaThe meridional cleavage of the sixth
division give a total of 64- cells and after
this stage the cleavages become some
what irregular .
Blastula
from side
W. M. of the blastula
Micromere
Blastocoel
Blastocoel
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The blastula of amphioxus
and its change in polarity
during gastrulation
The gastrula of amphioxus
with a remnant of theblastocoel still present at the
blastopore
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Gastrulation in Amphioxus
Sagittal half of an early
gastrula
Sagittal half of a later gastrula
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Sagittal half of a completed gastrula Dorsal half of a completed gastrula
Gastrulation in Amphioxus
Longitudinal section of a post
gastrula stage
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Gastrula of Amphioxus showing
progressive overgrowth of the the
ectoderm over the blastopore in
the formation of the neural folds
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Formation of the neural tube
T. s. and Stereogram of a part of a post-gastrulation stage.
T. S. to show the
separation of the
mesodermal
pouches
T. S. of a larva to
show the formation
of the coelom.
Stereogram to show
the arrangement of
the mesodermal
pouches.
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The gastrula of amphioxus.
The ectoderm has grown
over the blastopore in the
formation of the neurocoel.
The passage between theneurocoel and the
archentron is the neuroentric
canal.
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Amphioxus embryo with the neural tube, the notochord and the
mesodermal somites differentiated.
Longitudinal
section of a post
gastrula stage of
Amphioxus
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Young larvae of Amphioxus
Optical view of a young larva from the
dorsal aspect
Larval stage after opening of mouth and 3
gill slits.
Larval stage after opening 4 gill slits.
Embryo with the anterior gut diverticulum
Three gill slits
Four gill slits
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Fourteen somite larva of Amphioxus
Partly dissected young Amphioxus
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Gonads
A B
AB
Schematic section through the pharynx
of Amphioxus with special emphasis on
the mesodermal differentiation
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Diagrammatic transverse section through the larva of
Amphioxus during the formation of the atrium
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NucleusBlood vessels
OocyteFollicle cells
Stroma
A section of the ovary of the
frog containing young oocytes.
All nuclei are stll located in the
center of the oocytes and very
little yolk has been formed.
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