Cell Signaling and Cloning

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Cell Signaling and Cloning
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How do cells differentiate?

• Determination
• When a cell chooses a particular fate.
• Happens via cell signaling or asymmetrical cell
  division.
• Differentiation (when the cells actually begin to
  change/become different from one another)
• Caused by differential gene expression due to
  inductive signals
• Results in changes in cell function, shape
  (morphology), location
• A cell first becomes determined via induction,
  later it differentiates via induction

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Example of induction, determination, and
differentiation at work!

• The pressing question meiosis or mitosis?

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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.

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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.

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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!!!
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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
Germ cells
Meiosis
(diploid)
(diploid)
Gametes
(haploid)
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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
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How do sex cells become sex cells?

• What determines which cells become primordial
  germ cells in the early embryo?
• Asymmetrical cell division (in animals other than
  mammals and birds)
• Induction by neighboring cells (in mammals and
  birds)

Note this is a cell in the gastrula phase
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How do sex cells become sex cells?
1. Asymmetric cell division
sex cell molecule
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How do sex cells become sex cells?
1. Induction by neighboring cells
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How do sex cells become sex cells?
1. Induction by neighboring cells
Hey, you guys. Become a sex cell!
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How do sex cells become sex cells?

• In order for a sex cell (or any cell) to become a
  specialized cell
• That cell must become determined. This happens
  via asymmetrical division or inductive signals
  from other cells.
• Sometime later, the cell receive an inductive
  signal that tells it to begin to differentiate.

Note this is a cell in the gastrula phase
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An example of induction relating to body part
differentiation
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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!!!
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How do sex cells become sex cells?
1. Asymmetric cell division
sex cell molecule
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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.

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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.

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How can we prove that cells do not lose genetic
information as they differentiate?

• Cloning!

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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!

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Cloning Steps