Cell Division

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Cell Division

• Making New Cells

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Cell Division

• Cells come from pre-existing cells
• Cells need to reproduce!
• Single-celled organisms -- asexual reproduction.
• Multi-celled organisms growth.
• Cell Division Cytokinesis
• Nuclear Division
• Karyokinesis

3
Prokaryotes Binary Fission

• Simple

4
Eukaryotes more complex

• Chromosomes
• Chromosome Structure
• Chromatin
• Unduplicated
• Duplicated
• Chromosome Number
• Diploid
• Somatic cells (body cells)
• Haploid
• Germ cells (sex cells)

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Karyokinesis

• Mitosis
• Somatic cells (body cells)
• Cloning of genetic information exact copies
  made and distributed to new cells.
• Chromosome is retained (stays the same).
• Meiosis
• Germ cells (sex cells)
• Genetic information is shuffled new cells are
  each different.
• Chromosome is cut in half.

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Cell Cycle
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Chromosome Duplication

• During S-phase Synthesis
• Why?....
• So that later, the sister chromatids can separate
  into different (new) cells!

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Mitosis

• Prophase
• Metaphase
• Anaphase
• Telophase

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Prophase

• Nuclear Envelope Disappears
• Nucleolus Disappears
• Chromosomes Condense
• Chromatin? Chromosomes
• Spindle Fibers (Microtubules)
• Attach to Centromeres
• Attach to M.T.O.C.s

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Metaphase

• Chromosomes line up on the Metaphase Plate
• pushed pulled by the spindle fibers
• Spindle Apparatus well developed.

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Anaphase

• Chromosomes each broken at their centromeres
• spindle fibers on each side shorten
• New (unduplicated) chromosomes move toward the
  M.T.O.C.s

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Telophase

• Chromosomes stop moving when they reach the
  spindle poles (at the M.T.O.C.s)
• Nuclear Envelope re-forms (2x)
• Nucleolus re-forms (2x)
• Spindle fibers disappear
• Cytokinesis

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Cytokinesis
Cleavage Furrow divides the cells
Cell Plate divides the cells
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Meiosis

• Associated with Sex!
• Sexual Reproduction involves
• 2 parents
• Mixing of genetic information
• Life cycles, with MEIOSIS FERTILIZATION

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Life Cycles
HAPLOID
GAMETIC
DIPLOID
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Meiosis

• Mixing of Genetic Information
• Germ Cells (Sex Cells)
• Reduction in Chromosome Number
• Diploid ? Haploid
• 2 Divisions
• Meiosis I --- P,M,A,T
• Meiosis II --- P,M,A,T
• Results in 4 cells

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Meiosis I

• Prophase I
• Metaphase I
• Anaphase I
• Telophase I

• Pairing and separation of Homologous Chromosomes
• Crossing Over
• Independent Assortment
• 2n?1n

VARIATION!
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Meiosis I
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Meiosis II

• Prophase II
• Metaphase II
• Anaphase II
• Telophase II

• Separation of sister chromatids
• 1n?1n
• Results in 4 DIFFERENT cells.

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Meiosis II
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MEIOSIS -- Spermatogenesis
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MEIOSIS -- Oogenesis
Stimulated by Fertilization
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MITOSIS vs MEIOSIS
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