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Chapter 24
Development
Fertilization and the Stages of
Mitosis
What is embryonic
Development?
(I) Embryonic Development
In the early stages of development, the
organism is called an embryo
The process of embryonic
development includes:
1. Cleavage
2. Gastrulation
3. Differentiation
(A)
Cleavage
Cleavage is a series of mitotic
divisions where the cell increases in
cell number but NOT in cell size
Cleavage converts a single fertilized
egg (zygote) into many cells
As cleavage continues, the cells form a
hollow ball-type structure filled with
fluid. At this point, the embryo is called
a blastula
Stages of Development (Cleavage)
Zygote
2 cells
4 cells
2 layers
8 cells
Morula
Gastrula
3 layer
Blastula
Stages of Development (Cleavage)
(B)
Gastrulation
When the blastula
reaches several
hundred cells,
gastrulation occurs
In this stage, the cells
on one side of the
blastula push in and
form a two-layered
embryo called the
gastrula
Gastrula
The gastrula
consists of 3 layers:
a) endoderm – inner
layer of cells
b) mesoderm –middle
layer of cells
c) ectoderm - outer
layer of cells
(C) Differentiation
Differentiation- series of changes
that transform the unspecialized
embryonic cells into specialized
cells, tissues and organs
It is the three germ layers that give rise to all
the tissues and organs of an animal
Ectoderm
Mesoderm
Endoderm
Nervous system
bones and
muscles
lining of digestive
tract
blood and blood
vessels
lining of trachea,
bronchi, and
lungs
Digestive System
lining of mouth,
nostrils, and anus
epidermis of skin, reproductive and
excretory system
sweat glands,
hair, and nails
dermis layer of
skin
liver, pancreas
thyroid,
parathyroid
urinary bladder
(C) Growth and Differentiation
Differentiation- series of changes
that transform the unspecialized
embryonic cells into specialized
cells, tissues and organs
Growth- mot only are the number of
cells increasing, but the size of the
cells are increasing as well, and the
embryo as a whole starts to develop
Farmer Andy
Two types of Development
What are the 2 major types of
development?
Provide organisms that represent
each.
Two types of Development
External Development
 Fish,
amphibians, reptiles, birds
Internal Development
 Mammals
Farmer Andy
External Development
External Development
External Development
(B) Internal Development
Development occurs inside the female
Three types:
1.
2.
3.
Placental mammals
Marsupials
Monotremes
Egg Development
What is the difference between
these two eggs?
http://chickscope.beckman.uiuc.edu/explore/embryology/day08/graphics/e
Chicken Reproductive System
The ovaries appear like a bunch
of grapes and in an adult will
contain five to six developing egg
yolks.
The oviduct is divided into five
regions:




funnel or infundibulum, magnum
where albumen is secreted,
isthmus which secretes the shell
membranes,
uterus or shell gland,
the vagina which connects to the
cloaca.
Chicken eggs are incubated about
21 days before hatching.
Chicken
Reproductive
System
Structure of Egg
Consists of 4 membranes outside of the embryo
a)
chorion- outer-most membrane,
aids in gas exchange
b)
allantois- exchange of O2 and
CO2. Also a storage site for
wastes
c)
amnion- sac containing
d)
amniotic fluid which surround
the embryo, provides cushion
and acts as a shock absorber
yolk sac- source of food for the
embryo. Blood vessels in the
yolk sac transport food to the
developing embryo
Structure of Egg
Consists of 4 membranes outside of the embryo
a) chorion- outer-most
membrane, aids in gas
exchange
b) allantois- exchange of O2
and CO2. Also a storage site
for wastes
c)
d)
amnion- sac containing
amniotic fluid which
surround the embryo,
provides cushion and acts as
a shock absorber
yolk sac- source of food for
the embryo. Blood vessels in
the yolk sac transport food to
the developing embryo
Structure of Egg
Consists of 4 membranes outside of the embryo
a) chorion- outer-most
membrane, aids in gas
exchange
b) allantois- exchange of
O2 and CO2. Also a
storage site for wastes
c)
amnion- sac containing
amniotic fluid which
surround the embryo,
provides cushion and
acts as a shock absorber
d)
yolk sac- source of food
for the embryo. Blood
vessels in the yolk sac
transport food to the
Embryo
“Chicken Egg”
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
germinal disc
yolk
chalaza
shell
inner shell
membrane
outer shell
membrane
air cell yolk
membranes
outer layer of thin
albumen
dense albumen
inner layer of thin
albumen
chalaziferous layer
Fertilization
In the infertile egg, on the left, the nucleus is merely a light
spot on the yolk. The egg on the right is fertilized. In the
fertilized egg the ovum has fused with a sperm to begin
forming an embryo. By the time the fertilized egg is laid,
many cells are divided on the surface of the yolk and
formed a blastoderm. Can you see the difference between
the nucleus of the infertile egg and the blastoderm of the
fertilized egg? Both are indicated by the blue arrow.
Day 1
After one day in the
incubator, the small
white spot seen in
the fertilized egg
above has grown to
the size of a nickel
or a quarter.
Day 2
By 24 hours, pockets of
blood cells and developing
blood vessels, called blood
islands, begin to appear on
the surface of the yolk
along the outer edges of the
area opaca. These are
called the vitelline vessels.
At the same time, the heart
and vessels within the chick
embryo have begun to
develop.
Day 3
The embryo is the
question mark shape in
the center of the image. It
has grown considerably
since yesterday and the
anterior half of its body is
curved even more. The
heart, located inside the
anterior curve of the body
is much larger and more
developed than in
yesterday's photograph.
Day 4
At four days, nearly the
entire body of the embryo
has risen off the yolk and
turned to lay on its left
side. The upper portion of
the embryo is even more
curved and the tail is also
beginning to curve. The
heart is the dark red area
within the upper curve of
the embryo. Just a
fraction of an inch from
the heart, the eye is
visible. The large node
just above and to the right
of the eye is a portion of
the brain.
Day 5
Yolk
Eye of embryo
Albumen
Day 6
Yolk
Air space
Eye of embryo
Blood vessels
Day 7
A row of feather
germs appears on the
tail.
The sclera of the eye
begins to form.
Feather papillae
appear on the thigh.
The leg bends at the
knee.
Day 8
http://lancaster.unl.edu/4h/Embryology/Embryo.htm
Day 9
Welcome into the World
Hello World
I feel so naked
Hatching takes a lot out of You
1 hour
1 hour
20 Hours Old and they sleep
like teenagers
22 hours
Left-Overs aren't always good
Do Now 4/28
What are the four membranes found in
the adaptation for external
development??
(B) Internal Development
Development occurs inside the
female
Three types:
1.
2.
3.
Marsupials
Monotremes
Placental mammals
Marsupials
Are mammals that do not have a placenta
The embryo is born at a relatively premature
stage, and completes its development
externally in a pouch that contain mammary
glands
Examples are kangaroos, wombat,
Tasmanian devil and opossum
Marsupials
Marsupials
Fainting: Adaptations that my not
always work
Monotremes
They are the only mammals that hatch
their young from eggs.
The echidna and the platypus
Monotremes
Placental Mammals
These are animals, like humans, that contain a
structure called the uterus where the embryo
develops
Within the uterus, a specialized structure called
the placenta forms
It is through the placenta that the exchange of
nutrients, wastes, and respiratory gases
between the embryo and the mother take place
The umbilical cord, which contains blood
vessels, attaches the embryo to the placenta
Placental Mammals
Placental Mammals
Umbilical cord
And now to
Chapter 25,
Sexual Reproduction
and
Development in humans