Ch. 21 The Genetic Basis Of Development

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Ch. 21The Genetic Basis Of Development
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• I. Embryonic development
• A. Three processes make embryo development
  possible.
• Cell division - this would only produce
  identical cells
• Cell differentiation - cells become specialized
  in structure and function
• Morphogenesis - "creation of form" the physical
  process that gives an organism shape(this is like
  Power Rangers).

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• B. All three process overlap
• Morphogenesis allows for the basic body plan.
  Cell division and cell differentiation help to
  direct morphogensis.
• 2. Animals and plants have different
  morphogenesis
• Animals complete morphogenesis during embryonic
  development, and only grow for a certain juvenile
  period
• Plants have areas in which growth occurs
  throughout the life of the plant called meristems
  - perpetual embryonic regions. These occur at the
  tips of shoots and roots.

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• C. Model organisms used to study development
• 1. Frogs
• They have large eggs that are easy to see
• Fertilization and development happen outside the
  body.
• 2. Drosophilia, C.elegans, mouse, zebra fish
  (Decker has some of these) and for plants
  Arabidopsis.
• 3. Drosophilia has a 2 week generation time
• Caenorhabditis elegans can be grown easily in
  petri dishes and grows from zygote to adult in
  3.5 days. Its genome has been sequenced. They
  are also hermaphrodites

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• Mus musculus - mouse, there are now transgenic
  mice and mice who have had genes mutated, however
  embryo development is difficult to see.
• Danio rerio - zebrafish - easy to breed and
  generation time is longer than other models (2-4
  months) but early development is quick with a
  fish hatching two days after fertilization.
• Arabdopsis thaliana - a weed can produce 1000s of
  progeny in 8-10 weeks. They are easily
  transformed

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• Differential gene expression - we know that all
  cells have the same genes so how do certain genes
  get turned on and others not?
• Carrot cells taken from the root grew into normal
  carrot plants (a clone). Plant cells are
  totipotent- they have the potential to become any
  type of cell.
• Animal cells do not behave like this. Many can
  not even divide in culture at all.
• Attempts have been made to remove the nuclei from
  a frog egg cell and replace it with the nuclei
  from various stage tadpole cells. This has been
  marginally successful.

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• As embryonic development progresses potency of
  cells in animals changes.
• Dolly - The nucleus from an udder cell into a
  unfertilized egg cell ( the udder cells were
  stopped at the G1 checkpoint), then the eggs were
  implanted into surrogates. Her mitochondrial DNA
  is from the egg donor.
• Many clones do not develop normally because of
  DNA being methylated in the wrong places and
  disrupting gene expression.

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• Stem cells- unspecialized, continually
  reproducing, can differentiate into specialized
  cells of different types.
• Bone marrow- stem cells for different blood cells
• Recently discovered brain stem cells
• Pluripotent- cells that can become different
  types of cells.
• Embryos have stem cells that can be made
  immortal.

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• Different cell types make different proteins
• Specific cells make proteins that will direct
  their specific roles in the body.
• Cytoplasmic determinants from the mother direct
  the embryo development
• 3. Induction - signal molecules cause changes in
  developing cells by causing changes in gene
  expression.

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Transcription factors
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Animations of development
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Fetal development
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