cell signaling and cloning. how do cells differentiate? determination 1. when a cell “chooses” a...
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Cell Signaling and Cloning
How do cells differentiate?
Determination1. When a cell “chooses” a particular fate.
2. Happens via cell signaling or asymmetrical cell division.
Differentiation (when the cells actually begin to change/become different from one another)
1. Caused by differential gene expression due to inductive signals
2. Results in changes in cell function, shape (morphology), location
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”).
Primordial germ cells
Migrate to sex organs. Divide while migrating.
(diploid)
(diploid)Germ cells
Meiosis
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?”
= “sex cell molecule”
1. Asymmetric cell division
How do “sex cells” become “sex cells?”
1. Induction by neighboring cells
How do “sex cells” become “sex cells?”
1. Induction by neighboring cellsHey, 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?”
= “sex cell molecule”
1. Asymmetric cell division
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?
CloningClone: An exact genetic copy of an organism.
• Natural clones? Identical twins!
Cloning Steps