Transcript Cell Signaling and Cloning

Cell Signaling and
Cloning
How do cells differentiate?
D
etermination
When a cell “chooses” a particular fate.
2. Happens via cell signaling or asymmetrical cell division.
1.
D
ifferentiation (when the cells actually begin to
change/become different from one another)
Caused by differential gene expression due to inductive
signals
2. Results in changes in cell function, shape (morphology),
location
1.
A cell first becomes “determined” via induction, later
it differentiates via induction
Example of induction, determination,
and differentiation at work!
 The pressing question… meiosis or mitosis?
Meiosis or Mitosis?
 How do we go from gametes to a “full-fledged”
organism?
 Fertilization (egg + sperm meet) = zygote.
 Many rounds of cell division (we do need more than one
cell to perform all our many functions, after all!). This cell
division is called MITOSIS.
 Cells become specialized.
Meiosis or Mitosis?
 How do we go from gametes to a “full-fledged”
organism?
 Fertilization (egg + sperm meet) = zygote.
 Many rounds of cell division (we do need more than one
cell to perform all our many functions, after all!). This cell
division is called MITOSIS.
 Cells become specialized.
Meiosis or Mitosis?
 How do we go from gametes to a “full-fledged”
organism?
 Fertilization (egg + sperm meet) = zygote.
 Many rounds of cell division (we do need more than one
cell to perform all our many functions, after all!). This cell
division is called MITOSIS.
 Cells become specialized.
• Note: Up through the
BLASTULA stage in
humans, cells are
UNDIFFERENTIATED
Write this down!!!
How do “sex cells” become “sex
cells?”
 A germ cell is a cell that gives rise to sex cells. The very first germ
cells are called “primordial germ cells” and are initially located outside
of the sex organs. (Primordial means “original” or “the first”).
Migrate to sex
organs. Divide while
migrating.
Primordial
germ cells
(diploid)
Germ cells
(diploid)
Gametes
(haploid)
How do “sex cells” become “sex
cells?”
 Primordial germ cells originate near the cells in the developing
embryo that eventually become the gut.
Endoderm (gut)
*Note: this is a cell in
the “gastrula” phase
How do “sex cells” become “sex
cells?”
 What determines which cells
become primordial germ cells
in the early embryo?
1. Asymmetrical cell division
(in animals other than
mammals and birds)
2. Induction by neighboring
cells (in mammals and
birds)
*Note: this is a cell in
the “gastrula” phase
How do “sex cells” become “sex
cells?”
1. Asymmetric cell division
= “sex cell
molecule”
How do “sex cells” become “sex
cells?”
1. Induction by neighboring cells
How do “sex cells” become “sex
cells?”
1. Induction by neighboring cells
Hey, you guys.
Become a sex cell!
How do “sex cells” become “sex
cells?”
 In order for a sex cell (or any
cell) to become a specialized
cell…
1. That cell must become
determined. This happens via
asymmetrical division or
inductive signals from other
cells.
2. Sometime later, the cell receive
an inductive signal that tells it to
begin to differentiate.
*Note: this is a cell in
the “gastrula” phase
An example of induction relating to
body part differentiation
Meiosis or Mitosis?
 How do we go from gametes to a “full-fledged”
organism?
 Fertilization (egg + sperm meet) = zygote.
 Many rounds of cell division (we do need more than one
cell to perform all our many functions, after all!). This cell
division is called MITOSIS.
 Cells become specialized.
• Note: Up through the
BLASTULA stage in
humans, cells are
UNDIFFERENTIATED
Write this down!!!
How do “sex cells” become “sex
cells?”
1. Asymmetric cell division
= “sex cell
molecule”
Asymmetric Division
 Cytoplasmic determinants: substances in the
maternal gamete (egg) that affect the course of
early development by regulating gene expression,
which in turn affects cell fate.
 Cell fate: what a cell eventually becomes. When a
cell is said to be “determined,” its cell fate is
decided.
Differential gene expression is NOT
due to loss of genetic informaiton
 All of the somatic cells in an organism contain the
same DNA
 Different types of cells express different genes.
This is what makes cells different from one
another.
 All somatic cell nuclei contain all the information
needed to construct an entire organism.
How can we prove that cells do not lose
genetic information as they differentiate?
 Cloning!
How can we prove that cells do not lose
genetic information as they differentiate?
 Cloning
 Clone: An exact genetic copy of an organism.
• Natural clones? Identical twins!
Cloning Steps