Biology AHSGE

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Biology AHSGE

• Standard VI- Mitosis and Meiosis

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Biology AHSGE

• CONTENT STANDARD 6. Describe the roles of mitotic
  and meiotic divisions during reproduction,
  growth, and repair of cells.
• ELIGIBLE CONTENT
• A. Demonstrate an understanding of how meiosis
  leads to variation.
• B. Describe the role of meiosis in producing
  variation.
• C. Describe the role of meiosis in reproduction.
• D. Describe the role of mitosis in cell repair.
• E. Describe the role of mitosis in growth.
• F. Describe the role of both mitosis and meiosis.

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The Cell Cycle

• When a eukaryotic cell reaches its size limit, it
  divides.
• Cell Cycle- Reproduction by a cycle of growing
  and dividing.
• Three phases
• Interphase- Cell growth, maturity, DNA
  duplication, and prep for division
• Chromatin (relaxed form of DNA) strands make
  copies of themselves
• Mitosis- Nuclear material divides and moves to
  opposite sides of the cell
• Cytokinesis- Cytoplasm divides, and two identical
  daughter cells form

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The Cell Cycle
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The Cell Cycle and Mitosis

• Purposes
• Increase the number of cells as a young organism
  grows into the adult form
• Replace damaged cells
• Regulation Controlled by cyclins (proteins)
  binding to cyclin-dependent kinases (CDKs-
  enzymes)
• Cancer- Uncontrolled division and growth of cells
• Carcinogen- Known to cause cancer
• Apoptosis- Programmed cell death
• Stem cells- Unspecialized cells that can develop
  into specialized cells
• Embryonic stem cells- First 100-150 cells from a
  fertilized egg
• Adult stem cells- Found in various tissues may
  be used to maintain and repair those tissues

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Mitosis- Prophase

• Chromatin strands tighten (condense) into
  chromosomes
• Sister chromatids- Identical halfs of a
  chromosome
• Centromere- Center of attachment
• Nucleolus disappears
• Spindle Fibers appear and attach to opposite
  sides of centromeres and centrioles
• - Responsible for moving and arranging
  chromosomes
• Centrioles move to the poles
• - Spindle apparatus- Spindle fibers,
  centrioles and aster fibers (star-like
  microtubules of centriole)
• Nuclear envelope disappears

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Mitosis- Metaphase

• Sister chromatids are pulled by motor proteins
  along the spindle apparatus toward the center of
  the cell
• Chromosomes line up in the middle, or equator, of
  the cell

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Mitosis- Anaphase

• Microtubules of spindle apparatus shorten,
  pulling the chromosomes in half
• With the help of motor proteins, chromatid
  strands are pulled to opposite sides of the cell

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Mitosis- Telophase

• Chromatid strands arrive at ends of cell and
  decondense
• Two new nuclear membranes form around chromatin
• Nucleoli reappear
• Spindle apparatus disassembles

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Cytokinesis

• Cytoplasm divides resulting in two cells with
  identical nuclei
• In plants, a cell plate forms and new cell wall
  forms on each side
• Binary fission- In prokaryotes, DNA is duplicated
  and copies attach to cell membrane. Membrane
  grows and pulls apart DNA molecules. Cell
  completes fission, resulting in two identical
  cells.

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AHSGE Biology

• Standard VI- Mitosis and Meiosis

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Chromosomes

• Traits- Characteristics passed to offspring from
  parents
• Instructions found on chromosomes
• Genes- segments of DNA found on each chromosome
  approx. 1500 per chromosome
• Homologous Chromosomes- Pairs of chromosomes one
  from each parent
• Humans- 23 pairs 23 from each parent
• 46 total chromosomes

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Haploid Vs. Diploid

• Gametes- Sex cells with half the number of
  chromosomes
• Created to maintain the chromosome number from
  generation to generation
• Represented by symbol n
• Haploid- A cell with n number of chromosomes
• Human gametes- n 23
• Fertilization- Fusion of gametes
• Results in 2n zygote (fertilized egg cell)
• Diploid- A cell with 2n number of chromosomes
• Human somatic (regular body cells) cells- 2n 46

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Meiosis

• Forms gametes with genetic variation
• Spermatogenesis- process of producing sperm with
  half the number of chromosomes
• Undifferentiated- no flagellum
• Oogenesis- the creation of an ovum (egg cell)
• three polar bodies all die (incomplete egg cells)
• Reduction division- Reduces the number of
  chromosomes in half
• 2n ? n (Diploid to haploid)
• Occurs in reproductive structures of sexual
  organisms
• Involves two divisions Meiosis I and Meiosis II

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Meiosis I

• Cell undergoes Interphase
• Prophase I
• Homologous chromosomes condense and pair up
  (synapsis)
• Crossing over- segments or genes are exchanged
  during synapsis
• Centrioles move to opposite poles and spindle
  fibers attach to centromeres

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Crossing Over
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Meiosis I

• Metaphase I- Homologous chromosomes (pairs) line
  up at the equator
• Anaphase I- Homologous chromosomes separate and
  move towards opposite poles (disjunction)
• Reduces chromosome number from 2n to n
• Independent Assortment- random segregation and
  assortment of chromosomes during gametogenesis
  (production of gametes) aids in increasing
  genetic diversity

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Meiosis I

• Telophase I- Individual chromosomes arrive at
  opposite poles
• Cytokinesis occurs
• Nuclear membrane and nucleoli reappear
• Two new cells formed, each with new genetic
  variation

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Meiosis II

• Prophase II- Occurring in two cells
• Chromosomes condense
• Nucleolus disappears
• Spindle Fibers appear and attach to opposite
  sides of centromeres and centrioles
• - Centrioles move to the poles
• - Nuclear envelope disappears

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Meiosis II

• Metaphase II- Sister chromatids are pulled by
  motor proteins along the spindle apparatus to
  line up at the equator

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Meiosis II

• Anaphase II- Microtubules of spindle apparatus
  shorten, pulling the chromosomes in half and to
  opposite sides of the cell

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Meiosis II

• Telophase II
• Chromatid strands arrive at ends of cell and
  decondense
• Two new nuclear membranes form around chromatin
• Nucleoli reappear
• Spindle apparatus disassembles
• Cytokinesis occurs
• Four unique, haploid (n) gametes result

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