Download cells - Hicksville Public Schools

Aim: How does an embryo
develop inside the uterus?
How does the zygote form?
Zygote – A fertilized egg
What happens after fertilization?
The zygote begins to divide and travels to
the uterus, eventually implanting itself in
the uterus lining
What happens to the zygote after it
is formed?
Mitosis – causes the zygote to
repeatedly divide producing the
developing embryo.
Embryonic Development:
Fertilization
Mitosis
+
Sperm Egg
Zygote
Embryo- the stage in human
development from the first division of the
zygote until about nine weeks after
fertilization.
Cleavage
•The term used to
describe the early cell
division associated with
embryonic development.
•During this time period,
the number of cells
increase tremendously.
EARLY DEVELOPMENT
• Cleavage occurs
by mitosis
• 4 days = 50 cells
• 6-7 days = 100
cells and….
• Attaches to the
uterine wall
• (IMPLANTATION)
The result of cleavage is an embryo that
is …..
Not referring to size
Morula
A solid ball of cells which
moves towards the uterus
TWINS
• Fraternal Twins
• Two eggs were
released and both
fertilized by
different sperm.
• Not genetically
identical
• Identical Twins
• One egg fertilized
by one sperm.
• The embryo split
for some reason
around the morula
stage
Mitosis continues & the embryo
becomes……
Not a reference to size
A hollow ball of cells
Blastocyst
Cell division continues & the
cells of the embryo start to ….
• fold inwardly,
creating layers
to the embryo’s
shape
Gastrula
Gastrulation
• Three layers
• Each layer will
eventually form the
different organ systems
• Ectoderm (skin & CNS)
• Endoderm (GI Tract &
lungs)
• Mesoderm (muscle,
bone, blood)
CELL DIFFERENTIATION
Due to gene
expression, cells
undergo cellular
differentiation, in
which the cells
become increasingly
specialized in
structure & function.
Gene Expression
Genes that are
being expressed
are turned “on”
All genes of the genome are present in
every cell of the body, but only a small,
specific fraction of these genes are actually
expressed in each type of cell.
What makes some cells turn “on”
some genes while other genes are
“off”?
Environmental influences from within the
cell, from surrounding cells, or from
outside the organism.
Why are they different?
These seeds
carry the same
genes for
chlorophyll:
Grown
CC
in light
“ENVIRONMENT AFFECTS
GENE EXPRESSION”
Grown
in dark
Differentiation’s ultimate goal…
An embryo
with many
different
types of cells
Stem Cells
Stem cells
are
embryonic
cells that can
turn into any
type of cell in
the body
How can stem cells help us?
Can be used to
make any type of
cell that needs to
be replaced in
our bodies
Why is the use of stem cells so
controversial?
• They are often
taken from
fetuses.
• Opponents
believe that you
are killing a life.