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Chapter 24Chapter 24Development
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) CleavageCleavage 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 8 cells Morula Blastula
2 layers 3 layer
Gastrula
Stages of Development (Cleavage)
(B) GastrulationWhen the blastula reaches several hundred cells, gastrulation occursIn this stage, the cells on one side of the blastula push in and form a two-layered embryo called the gastrula
GastrulaThe 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
Digestive System
lining of mouth, nostrils, and anus
epidermis of skin, sweat glands, hair, and nails
bones and muscles
blood and blood vessels
reproductive and excretory system
dermis layer of skin
lining of digestive tract
lining of trachea, bronchi, and
lungs
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 organsGrowth- 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 DevelopmentWhat are the 2 major types of development?
Provide organisms that represent each.
Two types of DevelopmentExternal DevelopmentFish, amphibians, reptiles, birds
Internal DevelopmentMammals
Farmer Andy
External Development
External Development
External Development
(B) Internal Development
Development occurs inside the female
Three types:1. Placental mammals
2. Marsupials
3. Monotremes
What is the difference between these two eggs?
http://chickscope.beckman.uiuc.edu/explore/embryology/day08/graphics/embryo_chick.mov
Egg Development
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.
ChickenReproductive System
Structure of Egga) 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 developing embryo
Consists of 4 membranes outside of the embryo
Structure of Egga) 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 developing embryo
Consists of 4 membranes outside of the embryo
Structure of Egga) 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 developing embryo
Consists of 4 membranes outside of the embryo
Embryo
“Chicken Egg”1. germinal disc 2. yolk 3. chalaza 4. shell 5. inner shell membrane 6. outer shell membrane 7. air cell yolk membranes 8. outer layer of thin
albumen 9. dense albumen 10. inner layer of thin
albumen 11. 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 2By 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 3The 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 4/28Do Now 4/28What are the four membranes found in the adaptation for external development??
(B) Internal Development
Development occurs inside the female
Three types:1. Marsupials2. Monotremes3. Placental mammals
MarsupialsAre 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 Fainting: Adaptations that my not always worknot always work
MonotremesThey are the only mammals that hatch their young from eggs.
The echidna and the platypus
Monotremes
Placental MammalsThese 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
