CH 9: Mitosis

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CH 9 Mitosis CH 10 Meiosis

• How Cells Divide

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Overview Mitosis

• Mitosis
• Purpose
• growth and repair in multicelled organisms
• asexual reproduction in many organisms

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Overview Mitosis

• Mitosis
• An exact copy of the cells DNA is made, the
  copies separated, and each copy is put in a new
  cell.
• Mitosis occurs in somatic cells

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Mitosis

• One division.
• 1 cell ? 2 cells (called daughter cells)
• Daughter cells are genetically identical
• Chromosome number does not change.

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Mitosis

• Terms
• Mitosis division of the cells DNA and nucleus
• Cytokinesis division of the cytoplasm (cell)

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Mitosis

• Chromosome described/diagrammed
• Sister chromatids have identical DNA
• Centromere
• Kinetechore on centromere provides binding site
  for microtubules

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Chromosome Structure
Histone core is made up of 8 proteins
A nucleosome is 2 wraps of DNA around a histone
core
Histone core is shown in greater detail
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Cell Cycle

• Start with a newly formed cell
• Cell cycle describes the life cycle of a cell
  (page 154)
• Interphase
• G1, S, G2 or
• G0 (not shown in text)
• Path followed by cells that will not divide again
• Mitosis
• Cytokinesis

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Cell Cycle

• Interphase
• G 1 - period of cell growth
• S - DNA synthesis
• An exact copy is made of each chromosome
• Copies are joined at the ________
• G 2 cell prepares to divide
• e.g. centrioles duplicate in animal cells

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Mitosis

• Mitosis (division of nucleus) follows interphase
• 4 phases
• Prophase
• Metaphase
• Anaphase
• Telophase

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Prophase see pages 156/157

• Chromosomes condense, become visible under
  microscope
• Centrioles move towards poles (animal only)
• Nucleoli disappear
• Nuclear envelope breaks up and forms vesicles

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Plant Prophase

• Early prophase in a plant cell
• How would animal cell prophase differ from this?

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Metaphase

• Microtubules attach sister chromatids to
  opposite poles (to centrioles in animal)
• MT push and pull chromo to middle of cell
• MT running pole to pole elongate cell
• MT arranged as spindle fibers

Animal Metaphase
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Plant Metaphase

• Chromosomes tend to be messier in plant
  metaphase

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Anaphase

• Sister chromatids separate at centromere
• MT pull sister chromatids to opposite poles
• MT continue to elongate cell
• This also helps to separate chromatids

• Animal anaphase

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Plant Anaphase

• Separated sister chromatids clearly visible
• No ________

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Telophase and Cytokinesis

• Telophase starts when chromatids reach poles
• Goal is to make 2 new nuclei
• Chromo. unwind
• Nucleoli reappear
• Nuclear envelope reforms from vesicles
• _______ shown

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Cytokinesis

• Cytokinesis division of cytoplasm
• Begins during telophase
• Different in plant and animal cells

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Animal Cytokinesis

• Microfilaments wrap around the center of the cell
  and then contract
• Creates cleavage furrow
• Cell squeezed in 2
• Page 158

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Plant Cytokinesis

• Vesicles containing cell wall material line up
  across middle of cell
• Vesicles merge and form cell plate
• Cell plate grows until it divides the cell in 2

Cell plate
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Mitosis Review

• Comparison Plant and Animal Mitosis
• Mitosis
• Animal Cell Mitosis
• Plant Cell Mitosis

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Meiosis

• Goal of meiosis is to separate homologous
  chromosomes and produce gametes
• Homologous Chromosomes pair of chromosomes with
  genetic information about the same traits

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Overview Meiosis

• Meiosis
• Purpose of meiosis is to create gametes
• Egg and sperm in humans
• Needed for sexual reproduction
• Occurs in germ cells
• Ovaries and testes of humans

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MEIOSIS

• More on homologous chromosomes - see human
  karyotype on page 165

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Meiosis

• The process of meiosis requires 2 cellular
  divisions
• Chromosomes are duplicated prior to only the 1st
  division

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Related Terms

• Diploid cell 2 copies of each type of
  chromosome present (chromo. 2N)
• One copy came from moms egg and the other from
  dads sperm
• Human diploid number 46 (also say 2N 46)
• Haploid cell 1 copy of each type of chromosome
  present (chromo. N)
• Human haploid number 23 (N 23)

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Meiosis I

• Chromosomes duplicate prior to meiosis I
• Meiosis I see page 166
• Prophase I
• Metaphase I
• Anaphase I
• Telophase I

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Meiosis I

• Prophase I remember chromo. are duplicated
• Duplicated chromosomes form tetrads
• Tetrad pair of homologous chromosomes
• Crossing over may occur
• Homologous chromosomes exchange DNA segments
  see board
• Creates new combinations of DNA creates
  chromosomes that are a combination of your
  mothers DNA and your dads DNA

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Meiosis I

• Prophase I, continued
• Chromosomes condense
• Centrioles move towards opposite poles (animal
  only)
• Spindle fibers begin to assemble
• Nuclear envelope breaks down (always signals end
  of a prophase )

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Meiosis I

• Metaphase I
• Spindle fibers attach the homologous chromosomes
  to opposite poles/centrioles
• Spindle fibers push and pull the tetrads to the
  middle of the cell.

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Meiosis I

• Anaphase I
• Homologous chromosomes are separated and pulled
  to opposite poles by the spindle fibers
• Spindle fibers are made up of microtubules
• Microtubules running pole to pole lengthen and
  elongate the cell

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Meiosis I

• Telophase I and Cytokinesis
• Cell divides in two
• Animal cells - cleavage furrow squeezes cell in
  two
• Plant cells cell plate divides cell in two
• Nucleus does not reform

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Meiosis I

• At the end of meiosis I
• Homologous chromosomes have been separated
• Chromosomes are still duplicated
• Sister chromatids are no longer identical if
  crossing over has occurred
• Chromosome number has been cut in half (to
  haploid number)
• Count centromeres to count chromosomes

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Meiosis II

• Prophase II in each cell
• Centriole pairs separate and move to opposite
  poles (animal only)
• Spindle fibers attach to kinetechore (centromere)
  of each chromosome
• Remember chromosomes are still duplicated
• Notice that each chromo is attached to both poles
  (as in mitosis)

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Meiosis II

• Metaphase II
• Spindle fibers push and pull duplicated chromo.
  To the center of the cell

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Meiosis II

• Anaphase II
• Spindle fibers pull the sister chromatids apart
• One copy of each chromo moves to each pole
• Microtubules running pole to pole lengthen and
  elongate the cell

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Meiosis II

• Telophase II and Cytokinesis
• Nucleus reforms in each cell (4 cells in total)
• Cytoplasm divides
• Meiosis web link

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Meiosis II

• End result of meiosis
• 4 cells made
• Each cell has the haploid number of chromo.
• One copy of each type of chromo
• No two germ cells are identical due to
• independent assortment of homologous chromosomes
• crossing over during meiosis I

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Meiosis

• Two cellular/nuclear divisions
• 1st division separates homologous chromosomes
  (each in its duplicated state)
• 2nd division separates duplicated chromosomes
• 1 cell with 2N chromo ? 2 cells with N duplicated
  chromo? 4 cells with N chromo

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Meiosis Review

• Meiosis

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Cell Division Summary

• Pages 172 and 173 provide a terrific summary of
  the 2 types of cellular division.
• Given a picture of a phase of mitosis or meiosis
  you should be able to
• Identify the phase and division type
• Label as appropriate spindle fibers,
  centrioles, sister chromatids, homologous
  chromosomes, centromere/kinetechore, nuclear
  envelope

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Genetics Terms - Lab

• Homozygous
• Heterozygous
• Genotype
• Phenotype
• Dominant
• Recessive

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Genetics

• Recessive disorders (covered in lab)
• Co-dominant alleles blood type (covered in lab)

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Genetics

• Dominant disorders
• Example Huntingtons disease is dominant to
  being healthy

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Genetics

• Sex-linked disorders
• X-linked genetic information for the trait is
  located on the X chromosome
• no genetic info about the trait on the Y chromo
• Examples Hemophilia and colorblindness
• Y-linked (not many known)
• Allele for hairy ears is y-linked