Animals
Tissue Development
Day 0: Conception
Sperm (n) fertilizes the egg (n)
The cell is now called a Zygote
now Diploid in number (2n)
Day 1: First Cleavage
1 cell becomes 2 cells
through a process called mitosis
Day 2: Second Cleavage
2 cells becomes 4 cells
Day 3: 4 cells becomes 8 cells
can test fore genetic diseases
as early as this stage if conception
was IVF (in vitro fertilization)
Day 4: 16 – 32 cells
Solid ball of cells is called a morula
mass
Day 6 - 7: Blastocyst attaches itself to the endometrium
(the lining of the uterine) = Implantation
Blastocyst secretes HCG (human chorionic gonatotropin)
• Pregnancy tests measure the amount of this hormone
• Stimulates the release of estrogen and progesterone preventing menstration
• Causes “Morning Sickness” in some women
Day 7 - 10: Gastrulation: major cellular reorganization into
3 germ (tissue) layers
• Ectoderm – (outer) skin, nervous system
• Mesoderm – (middle) muscles and bones
• Endoderm – (inner) lining of gut and internal organs
All the cells have the same DNA, however, different cells
begin to “turn on” or “express” different genes to become
different organs
Embroyonic Layers
1. Ectoderm
diploblastic
2. Endoderm
triploblastic
3. Mesoderm
Day 10 - 14: Pregnancy is established:
• Chorion (placenta) begins to form
• Amniotic fluid begins to form
• Embryo starts to form from embryonic disc
• Yolk sac – makes blood & germ cells
Day 15 - 21: Emergence of a vertebrate body plan:
Primitive streak:
• Neural groove – future spinal cord and brain (CNS)
• Somites – bands of tissue to become muscle & bone
• Pharyngeal arches – future neck, face, mouth, nose
Day 21… Week 3 – Week 8 (Embryo):
Development of all organ systems
Week 8 Embryo – is now called a Fetus:
Gender differentiation begins
SRY gene present and functioning =
ovaries—testes; labium—scrotum; cliteris—penis
Pharyngeal arches
The diagram above shows a developing worm embryo at the four-cell stage.
Experiments have shown that when cell 3 divides, the anterior daughter cell gives rise to
muscle and gonads and the posterior daughter cell gives rise to the intestine.
However, if the cells of the embryo are separated from one another early during the
four-cell stage, no intestine will form. Other experiments have shown that if cell 3 & cell 4
are recombined after the initial separation, the posterior daughter cell of cell 3 will once
again give rise to normal intestine.
Do you think…
- Cell 4 transfers genetic material to cell 3, which directs the development of intestinal cells?
- Cell 3 passes an electrical signal to cell 4, which induces differentiation in cell 4?
- The plasma membrane of cell 4 interacts with the plasma membrane of the posterior
portion of cell 3, causing invaginations that become microvilli?
- A cell surface protein on cell 4 signals cell 3 to induce formation of the worm’s intestine?
Cells communicate with each other in a variety of ways - most of which involves proteins embedded in their cell
membranes. As it turns out, there is a protein in the worm’s cell #4 that signals cell 3 to begin intestinal formation.
Teratogen: an agent or factor that causes malformation of an embryo
Chordata
• Vertebrates
– fish, amphibians, reptiles, birds, mammals
– internal bony skeleton
hollow dorsal
• backbone encasing
spinal column
• skull-encased brain
Oh, look…
your first
baby picture!
nerve cord
becomes brain
& spinal cord
becomes gills or
Eustachian tube
pharyngeal
pouches
becomes tail
or tailbone
postanal
tail
becomes
vertebrae
notochord
Animal Evolution
exoskeleton
backbone
segmentation
endoskeleton
True coelom
body cavity
asymmetry
radial symmetry
Independent cells
multicellularity
Ancestral Protist
bilateral symmetry
tissues
Animal Evolution
Cnidaria
Porifera
sponges
jellyfish
Nematoda
Platyhelminthes
Echinoderm
Arthropoda
Mollusca
segmented insects
spiders
roundworms
Seastar
mollusks
worms
flatworms
exoskeleton
Annelida
Chordata
vertebrates
backbone
segmentation
endoskeleton
True coelom
body cavity
asymmetry
radial symmetry
Independent cells
multicellularity
Ancestral Protist
bilateral symmetry
tissues
Embroyonic Layers
1. Ectoderm
diploblastic
2. Endoderm
triploblastic
3. Mesoderm
Body Cavity
How much is
the digestive
tract separated
from the rest of
the body?
ectoderm
mesoderm
endoderm
acoelomate
ectoderm
mesoderm
endoderm
pseudocoelomate
pseudocoel
• 3 body layers
– ectoderm
– mesoderm
– endoderm
ectoderm
mesoderm
coelom cavity
coelomate
endoderm
Embroyonic Layers
1. Ectoderm
2. Endoderm
3. Mesoderm
What embryonic layers develop into these structures?
1. Skin/epidermis
Skin/Epidermis 7. Lungs
Lungs
13. Nerves
Nerves
2. Muscles
Muscles
8. Neural
Neuraltube
tube
14. Liver
Liver
3. Kidneys
Kidneys
9. Reproductive
Reproductiveorgans
organs
15. Hair
Hair
4. Spinal
Spinal cord
cord
10. Notochord
Notochord
16. Bones
5. Intestines
Intestines
11. Blood vessels
17. Eye
6. Heart
Heart
12. Tooth
Tooth enamel
enamel
18. ??
sequence of stages during embryogenesis
Using these terms, answer the questions below:
Fertilization - Zygote
Cleavage - Embryo
Blastula
Gastrulation
Neuralization
a. This process establishes the primary germ layers
b. Cells migrate over the dorsal lip of the blastopore
c. number of cells increases, but there is no increase in total cell mass and there is little or
no differentiation
d. Two haploid cells fuse to form a diploid cell
sequence of stages during embryogenesis
Using these terms, answer the questions below:
Fertilization - Zygote
Cleavage - Embryo
Blastula
Gastrulation
Neuralization
a. This process establishes the primary germ layers Gastrulation
b. Cells migrate over the dorsal lip of the blastopore
Blastula
c. number of cells increases, but there is no increase in total cell mass and there is little or
no differentiation
Cleavage
d. Two haploid cells fuse to form a diploid cell Fertilization