Meiosis

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Meiosis
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• Image found on
• www.accessexcellence.org

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Why is there Meiosis?

• TO MAKE SEX CELLS WHICH ARE HAPLOID

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MEIOSIS 1

• As in mitosis, meiosis 1 is preceded by the
  synthesis of DNA and replication of chromosomes
  So we could call this Interphase 1

• Synapsis the process when homologous chromosomes
  come together
• Tetrad the structure formed when the
  chromosomes come together . x structure
• Chiasmata-the site of crossing over of non sister
  chromatids

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Prophase I

• The chromatin begins to coil into short rods and
  homologous chromosomes are formed
• Spindle fibers appear and nucleus brakes down
• The nuclear membrane is gone at end. Image found
  taggart.glg.msu.edu/bs110/meiosis.htm

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Metaphase I

• Tetrads become attached to spindle fibers
• Crossing Over occurs
• Image may be found on www.mnsu.edu/.../sourceofgen
  etic variation.html

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Anaphase I

• Homologous chromosomes separate
• Reducing process
• 2n to n
• Next two slides Images found on
  library.thinkquest.org//media/prophase-1.gif

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Telophase I

• The chromosomes reach the end of the cell.
  Cytokinesis takes place. Two daughter cells are
  produced
• Nucleus,nuclear membrane, cytoskeleton, nucleolus
  reappear
• DNA uncoils

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Meiosis II

• The following 6 slides have pictures found on
  www.pbs.org/wgbh/nova/miracle/divi_text_09.html

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Interphase II

• NO DNA replication

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Prophase II

• DNA coils
• Mitotic spindle forms
• Nucleolus disappears
• Nuclear membrane disappears
• Nucleus disappears

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Metaphase II

• Sister chromatids line up at the equator

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Anaphase II

• Centromere splits
• Chromosomes are pulled to opposite poles

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Telophase II

• Mitotic spindles break down, nucleolus, nuclear
  membrane, nucleus, reforms
• DNA uncoils
• Cytokinesis

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What is the result of Meiosis?

• 4 daughter cells
• haploid

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Spermatogenesis

• The production of sperm cells
• Image found on users.rcn.com//S/Sexual_Reproducti
  on.html

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OOGENESIS

• Production of mature egg cells
• During meiosis the cytoplasm of original cell is
  divided unequally between new cells
• One cell gets most of cytoplasm. This becomes
  the egg and the other 3 cells are called polar
  bodies, which eventually degenerate
• Image found on www.columbia.edu/.../hand-1.htmlhan
  d-1a.html