Transcript Development for Class

Animal Reproduction
&
Development
AP Biology
2007-2008
Oogenesis
What is the
advantage of
this development
system?
 Unequal meiotic divisions



unequal distribution
of cytoplasm
1 egg
2 polar bodies
Meiosis 1 completed
during egg maturation
ovulation
Meiosis 2 completed
triggered by fertilization
AP Biology
Put all your egg
in one basket!
Fertilization





AP Biology
fertilization
cleavage
gastrulation
neurulation
organogenesis
Fertilization
 Joining of sperm & egg

AP Biology
sperm head (nucleus) enters egg
Mammalian Fertilization
1. Sperm binds to receptors in zona pellucida (extracellular
matrix of egg)
2. Acrosomal reaction: sperm releases hydrolytic enzymes
to digest z.p.
(Sea Urchins) Depolarization of membrane: prevent
other sperm from binding = fast block to polyspermy
3. Sperm + Egg Fuse
4. Cortical reaction: sperm + egg fusion triggers release of
Ca2+

cortical granules fuse with z.p.  z.p.
hardens to form fertilization envelope = slow
block to polyspermy
5. Ca2+ release also triggers activation of the egg
AP Biology
Cleavage
 Repeated mitotic divisions of zygote
1st step to becoming multicellular
 unequal divisions establishes body plan

 different cells receive different portions of egg
cytoplasm & therefore different regulatory signals
AP Biology
 The eggs and zygotes of many animals,
except mammals, have a definite polarity
 The polarity is defined by distribution of
yolk, with the vegetal pole having the most
yolk
 The development of body axes in frogs is
influenced by the egg’s polarity
AP Biology
LE 47-8
Point of
sperm entry
Animal
hemisphere
Vegetal
hemisphere
Point of
sperm
entry
Anterior
Right
Ventral
Gray
crescent
Posterior
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Vegetal pole
Future
dorsal
side of
tadpole
First
cleavage
Dorsal
Left
Body axes
Animal pole
Establishing the axes
 Cleavage planes usually follow a pattern that
is relative to the zygote’s animal and vegetal
poles
AP Biology
LE 47-9
Zygote
0.25 mm
2-cell
stage
forming
4-cell
stage
forming
Eight-cell stage (viewed
from the animal pole)
8-cell
stage
0.25 mm
Animal pole
Blastula
(cross
section)
Blastocoel
Vegetal pole
Blastula (at least 128 cells)
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Cleavage
 zygote  morula  blastula

establishes future development
zygote
gastrulation
AP
Biology
morula
blastula
Gastrulation
gastrulation in
primitive chordates
 Establish 3 cell layers

ectoderm
 outer body tissues
 skin, nails, teeth
 nerves, eyes, lining of mouth

mesoderm
ectoderm
 middle tissues
 blood & lymph, bone & notochord,
mesoderm
muscle
 excretory & reproductive systems

endoderm
 inner lining
 digestive system
 lining of respiratory, excretory &
reproductive systems
AP Biology
protostome
vs. deuterostome
endoderm
Testing…
All of the following correctly describe the fate of the
embryonic layers of a vertebrate EXCEPT
A. neural tube and epidermis develop from ectoderm
B. linings of digestive organs and lungs develop from
endoderm
C. notochord and kidneys develop from endoderm
D. skeletal muscles and heart develop from mesoderm
E. reproductive organs and blood vessels develop from
mesoderm
AP Biology
Cleavage
 If spiral (diagonal cell division) and determinate
= protostome development
 The develop fate of each cell is determined
early on (1,2nd cell division)
 The blastopore becomes the mouth
 If radial (Up/down side/side cell division) and
indeterminate = deuterostome development
 Cells in the early embryo can develop into a
complete embryo
 The blastopore becomes the anus
AP Biology
Fig. 32-9
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderm,
chordates)
Eight-cell stage
Eight-cell stage
Spiral and determinate
(a) Cleavage
Radial and indeterminate
(b) Coelom formation
Key
Coelom
Ectoderm
Mesoderm
Endoderm
Archenteron
Coelom
Mesoderm
Blastopore
Blastopore
Solid masses of mesoderm
split and form coelom.
Mesoderm
Folds of archenteron
form coelom.
Anus
Mouth
(c) Fate of the blastopore
Digestive tube
Mouth
Mouth develops from blastopore.
AP Biology
Anus
Anus develops from blastopore.
Neurulation
 Formation of notochord & neural tube

develop into nervous system
Neural tube
Notochord
develops into
vertebral column
AP Biology
develops into CNS
(brain & spinal cord)
Patterns of development
 Cytoplasmic determinants: chemical signals


such as mRNAs and transcription factors,
influence pattern of cleavage
Induction: interaction among cells that
influences their fate, cause changes in
gene expression
Totipotent cells: capable of developing into
all the different cell types

AP Biology
all cells of mammalian embryos are
totipotent until the 16-cell stage
Organogenesis
Mammalian embryo
Umbilical blood vessels
Chorion
Bird embryo
Amnion
Yolk
sac
Allantois
Fetal blood vessels
Placenta
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Maternal blood vessels
Placenta
 Materials exchange across membranes
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Human fetal development
4 weeks
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7 weeks
Human fetal development
10 weeks
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Human fetal development
12
weeks
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20 weeks
Human fetal development
 The fetus just spends much of the 2nd &
3rd trimesters just growing
…and doing various flip-turns & kicks
inside amniotic fluid
Week 20
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Human fetal development
 24 weeks (6 months; 2nd trimester)
fetus is covered
with fine, downy
hair called
lanugo. Its skin
is protected by
a waxy material
called vernix
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Human fetal development
 30 weeks (7.5 months)
umbilical cord
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Getting crowded in there!!
 32 weeks (8 months)
The fetus
sleeps 90-95%
of the day &
sometimes
experiences
REM sleep, an
indication of
dreaming
AP Biology
positive feedback
Birth
AP Biology
Birth (36 weeks)
Intestine
Placenta
Umbilical
cord
Wall of
uterus
Bladder
AP
Cervix
Vagina
Biology
The end of the journey!
And you think
9 months of
AP Bio is hard!
AP Biology