CELL DIVISION

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CELL DIVISION

• Turn in pg. 15 in the Resource Book.

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CELL DIVISION

• Necessary for GROWTH and REPAIR
• Two major processes of cell division.
• Left side MITOSIS
• Right side - MEIOSIS

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MITOSIS

• Occurs in body cells. Basically all your cells
  except the sex cells.
• Contains a full set of chromosomes. (2n) Diploid.
• The (n) value depends on the organism. In
  humans, (n) is equal to 23.
• Results in two identical daughter cells.

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Mitosis has 5 stages

• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase

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Interphase

• Chromosomes form thin strands called CHROMATIN
  which has DNA in structures called NUCLEOSOMES.
• Can be divided into three phases G1, S, and G2.
• Cell spends most of its time in interphase

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Prophase

• The CENTRIOLE divides and aids in spindle
  formation.
• The chromatin reforms into chomosomes.

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What is a chromosome?
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Metaphase

• Chromosomes line up at the middle.

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Anaphase

• The CHROMOSOMES separate.
• The centrioles pull the chromosomes to opposite
  ends of the cell.

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Telophase

• The SPINDLE FIBERS and CENTRIOLES disappear.
• Result in a DIPLOID (2n) number of chromosomes.
• Process of Cytokinesis.

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MEIOSIS

• Occurs in sex cells (egg and sperm)
• Contains a half set of chromosomes. (n) Haploid.
• Results in four different cells.
• Germ cells unite to form a ZYGOTE (fertilized
  egg)

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Meiosis has 8 stages

• Meiosis I CHROMOSOMES carry genetic information
  and separate. They line up as TETRADS. (which
  are pairs of chromatids)

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Meiosis has 8 stages

• Meosis II The CHROMATID PAIRS divide.
• FOUR cells are finally formed.
• Each cell is a HAPLOID (n)

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Meiosis

• In females, the process of meiosis is called
  OOGENESIS. It results in one large egg cell and
  three small polar bodies.
• In males, the process of meiosis is called
  SPERMATOGENESIS. It results in four equal sperm
  cells.

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ASEXUAL CELL DIVISION

• The two major types of asexual cell division are
  BUDDING and BINARY FISSION.
• Binary fission is the splitting INTO TWO where
  budding is when the young grow off the adult.
• Both result in a IDENTICAL DAUGHTER CELLS.
  Similar as in Mitosis.

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What is a zygote?

• A zygote is a fertilized egg.
• A zygote goes through stages of cleavage.
• You will need to know the following stages
• 1. BLASTOMERE four cell stage

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Stages of Cleavage cont.

• 2. BLASTULA A hollow ball made out of a single
  layer of cells.

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Stages of Cleavage cont.

• 3. GASTRULA The hollow ball folds in on itself
  to form three layers of cells/tissues.

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THREE EMBRYONIC TISSUE LAYERS

• 1. ECTODERM gives rise to the skin and nervous
  system.
• 2. ENDODERM (Entoderm) gives rise to the
  digestive tract.
• 3. MESODERM gives rise to the muscles, bones,
  and blood.

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ANY QUESTIONS????