Chapter%207%20Meiosis

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Chapter 7 Meiosis
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Meiosis

• Forms haploid gamete or spore cells
• Type of cell division that halves the number of
  chromosomes
• Creates 4 genetically different cells

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Steps to Meiosis I

• Prophase I Chromosomes condense, nuclear
  membrane breaks down, homologous chromosomes pair
  up and crossing-over occurs
• Crossing-over when homologous chromosome pairs
  exchange genetic material

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• http//www.zerobio.com/crossing_over.htm

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Metaphase I

• Pairs of homologous chromosomes line up together
  (like holding hands)

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Anaphase I

• Pairs separate (NOT CHROMATIDS) and are pulled to
  opposite ends of the cell

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Telophase I

• Chromosomes gather at the poles
• Cytokinesis then occurs
• DNA does not replicate to start Meiosis II

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Prophase II

• New spindle forms

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Metaphase II

• Chromosomes line up along the middle of the cell
  (just like Mitosis)

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Anaphase II

• Centromeres divide, chromatids separate, and move
  towards the poles of the cell

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• Telophase II Nuclear membrane forms around each
  set of chromosomes
• Cytokinesis occurs

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• http//highered.mcgraw-hill.com/sites/0072437316/s
  tudent_view0/chapter12/animations.html

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• http//www.johnkyrk.com/meiosis.html

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Genetic Diversity

• Meiosis contributes to genetic diversity
• Makes sure all organisms are genetically
  different

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Independent Assortment

• The random distribution of homologous chromosomes
  during Meiosis

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Crossing-Over

• DNA exchanged between homologous chromosomes
  during Prophase I

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Random Fertilization

• Random sperm cell fuses with a random egg cell

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• http//biog-101-104.bio.cornell.edu/BioG101_104/tu
  torials/cell_division/CDCK/cdck.html

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Oogenesis

• Process that creates female egg cells
• Of the four haploid cells created during Meiosis,
  three will die as polar bodies and one will
  survive as an egg cell

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Spermatogenesis

• Process that creates male sperm cells
• All four haploid gamete cells will develop into
  sperm cells

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7-2 Sexual Reproduction

• Asexual One parent
• Creates offspring that are clones
• Sexual Reproduction two parents
• Creates genetically different offspring

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Advantages for Each

• Asexual allows organisms to produce many
  offspring in a short amount of time
• Sexual reproduction creates genetic diversity

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Disadvantages for Both

• Asexual creates very little genetic diversity
• Sexually reproducing organisms depend on finding
  mates (takes time and NRG)

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Alternation of Generations

• Organisms cycle through diploid and haploid life
  stages
• Haploid Life Cycle haploid cells occupy the
  major portion of the life cycle (protists, fungi)

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• Diploid Life Cycle - adult individuals are
  diploid, gametes are the only haploid cells
  (animals)
• Alternation of Generations plants, algae, and
  some protists alternate between a haploid and
  diploid phase
• Sporophyte diploid phase when spores are made

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• Gametophyte - haploid phase where gametes are
  made

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