CHAPTER 9 Chromosomes, the Cell Cycle, and Cell Division

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CHAPTER 9Chromosomes, the Cell Cycle, and Cell
Division
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Chapter 9 Chromosomes, the Cell Cycle, and Cell
Division

• Systems of Cell Reproduction
• Interphase and the Control of Cell Division
• Eukaryotic Chromosomes
• Mitosis Distributing Exact Copies of Genetic
  Information

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Chapter 9 Chromosomes, the Cell Cycle, and Cell
Division

• Cytokinesis The Division of the Cytoplasm
• Reproduction Sexual and Asexual
• Meiosis A Pair of Nuclear Divisions
• Meiotic Errors
• Cell Death

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Cell Division

• Cell division is necessary for reproduction,
  growth, and repair of an organism.
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Systems of Cell Reproduction

• Cell division must be initiated by a reproductive
  signal and consists of three steps
• replication of the genetic material (DNA)
• partitioning of the two DNA molecules
• division of the cytoplasm
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Systems of Cell Reproduction

• In prokaryotes, cellular DNA is a single
  molecule, or chromosome.
• Prokaryotes reproduce by cell fission.
• Review Figure 9.3
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Figure 9.3
figure 09-03.jpg

• Figure 9.3

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Systems of Cell Reproduction

• In eukaryotes, nuclei divide by either mitosis or
  meiosis.
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Interphase and the Control of Cell Division

• The mitotic cell cycle has two main phases
  interphase and mitosis.
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Interphase and the Control of Cell Division

• During most of the cell cycle the cell is in
  interphase, which is divided into three
  subphases S, G1, and G2.
• DNA is replicated during S phase.
• Review Figure 9.4
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Figure 9.4
figure 09-04.jpg

• Figure 9.4

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Interphase and the Control of Cell Division

• Cyclin-Cdk complexes regulate the passage of
  cells from G1 into S phase and from G2 into M
  phase.
• Review Figure 9.5
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Figure 9.5
figure 09-05.jpg

• Figure 9.5

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Interphase and the Control of Cell Division

• In addition to the internal cyclin-Cdk complexes,
  controls external to the cell, such as growth
  factors and hormones, can also stimulate a
  division cycle.
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Eukaryotic Chromosomes

• Chromosomes contain DNA and proteins.
• At mitosis, chromosomes initially appear double
  because two sister chromatids are held together
  at the centromere.
• Each sister chromatid consists of one
  double-stranded DNA molecule complexed with
  proteins and referred to as chromatin.
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Eukaryotic Chromosomes

• During interphase, DNA in chromatin is wound
  around histone cores to form nucleosomes.
• DNA folds repeatedly, packing within the nucleus.
  When mitotic chromosomes form, it folds even
  more.
• Review Figure 9.7
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Figure 9.7
figure 09-07.jpg

• Figure 9.7

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Mitosis Distributing Exact Copies of Genetic
Information

• After DNA is replicated during S phase, the first
  sign of mitosis is the separation of centrosomes,
  which initiate microtubule formation for the
  spindle.
• Review Figure 9.9
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Figure 9.9
figure 09-09.jpg

• Figure 9.9

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Mitosis Distributing Exact Copies of Genetic
Information

• Mitosis can be divided into phases
• prophase
• metaphase
• anaphase
• telophase
• Review Figure 9.8
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Figure 9.8 Part 1
figure 09-08a.jpg

• Figure 9.8 Part 1

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Figure 9.8 Part 2
figure 09-08b.jpg

• Figure 9.8 Part 2

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Mitosis Distributing Exact Copies of Genetic
Information

• During prophase, the chromosomes condense and
  appear as paired chromatids.
• Centrioles move to the poles.
• Spindle fibers form.
• Chromosomes move toward the middle of the cell.
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Mitosis Distributing Exact Copies of Genetic
Information

• In Metaphase, chromosomes line up on the equator
  and their centromeres attach to a spindle fiber.
  
• At Anaphase, chromatid pairs separate and
  migrates to opposite poles.
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Mitosis Distributing Exact Copies of Genetic
Information

• During telophase, the chromosomes uncoil.
• The nuclear membranes re-form, producing two
  nuclei identical to each other and the original
  cell.
• The cytoplasm then divides.
• Review Figure 9.8
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Cytokinesis The Division of the Cytoplasm

• Cytokinesis usually follows nuclear division.
• Animal cells pinch in to divide cytoplasm.
• In plant a new cell wall is built.
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Reproduction Sexual and Asexual

• Asexual reproduction produces an organism
  genetically identical to the parent.
• Any genetic variety is the result of mutations.
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Reproduction Sexual and Asexual

• In sexual reproduction, two haploid gametesone
  from each parentunite in fertilization to form a
  genetically unique, diploid zygote.
• Review Figure 9.12
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Figure 9.12 Part 1
figure 09-12a.jpg

• Figure 9.12 Part 1

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Figure 9.12 Part 2
figure 09-12b.jpg

• Figure 9.12 Part 2

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Figure 9.12 Part 3
figure 09-12c.jpg

• Figure 9.12 Part 3

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Reproduction Sexual and Asexual

• In sexually reproducing organisms, certain cells
  in the adult undergo meiosis, whereby a diploid
  cell produces haploid gametes.
• Each gamete contains a random mix of one of each
  pair of homologous chromosomes from the parent.
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Reproduction Sexual and Asexual

• The number, shapes, and sizes of the chromosomes
  constitute the karyotype of an organism.
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Meiosis A Pair of Nuclear Divisions

• Meiosis reduces the chromosome number from
  diploid to haploid and ensures that each haploid
  cell contains one member of each chromosome pair.
  
• It consists of two nuclear divisions.
• Review Figure 9.14
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Figure 9.14 Part 1
figure 09-14a.jpg

• Figure 9.14 Part 1

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Figure 9.14 Part 2
figure 09-14b.jpg

• Figure 9.14 Part 2

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Meiosis A Pair of Nuclear Divisions

• During prophase I homologous chromosomes pair,
  and crossing over occurs between homologs.
• In metaphase I, the paired homologs line up at
  the equatorial.
• Both chromosomes attach to the same spindle
  fiber.
• In anaphase I, chromosome pairs split and move to
  the poles.
• After Telophase I, there are two haploid cells.
• Review Figures 9.14, 9.16
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Figure 9.16
figure 09-16.jpg

• Figure 9.16

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Meiosis A Pair of Nuclear Divisions

• In meiosis II, the sister chromatids separate.
• No DNA replication precedes this division.
• The result of meiosis is four haploid cells.
• Review Figures 9.14, 9.17
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Figure 9.17 Part 1
figure 09-17a.jpg

• Figure 9.17 Part 1

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Figure 9.17 Part 2
figure 09-17b.jpg

• Figure 9.17 Part 2

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Meiosis A Pair of Nuclear Divisions

• Both crossing over and the independent assortment
  of chromosomes ensure that the genetic
  composition of gametes is different from that of
  the parent and other gametes.
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Meiotic Errors

• In non-disjunction, one member of a homologous
  pair of chromosomes fails to separate from the
  other, and both go to the same pole.
• Fertilization with a normal haploid gamete
  results in aneuploidy and genetic abnormalities
  that are invariably harmful or lethal.
• Review Figure 9.18
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Figure 9.18
figure 09-18.jpg

• Figure 9.18

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Cell Death

• Cells may die by necrosis or may self-destruct by
  apoptosis, a genetically programmed series of
  events that includes the detachment of the cell
  from its neighbors and the fragmentation of its
  nuclear DNA.
• Review Figure 9.19
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Figure 9.19
figure 09-19.jpg

• Figure 9.19