The Cell Cycle, Mitosis

1
The Cell Cycle, Mitosis Meiosis

• Chapter 5 (pages 200-201)
• Chapter 7 (252-253)

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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. Figure 9.4

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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 09-08a.jpg
Figure 9.8 Part 1
Figure 9.8 Part 1
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figure 09-08b.jpg
Figure 9.8 Part 2
Figure 9.8 Part 2
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Mitosis Distributing Exact Copies of Genetic
Information

• Prophase chromosomes condense and appear as
  paired sister chromatids. Chromosomes move toward
  the middle of the spindle
• Metaphase they gather at the middle of the cell,
  their centromeres on the equatorial plate

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Mitosis Distributing Exact Copies of Genetic
Information

• End of Metaphase Centromeres separate.
• Anaphase daughter chromosomes migrate to its
  pole along the microtubule track.
• Telophase chromosomes unwind, nuclear envelopes
  and nucleoli re-form.
• Product two nuclei with identical chromosomes
  are formed.

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Cytokinesis The Division of the Cytoplasm

• Cytokinosis Cell Division. Animal
  cells-cytoplasm usually divides by plasma
  membrane furrowing caused by contraction of
  cytoplasmic microfilaments. Plant cells-
  cytokinesis by vesicle fusion and the synthesis
  of new cell wall material.
• Diploid Cell gives rise to two Diploid Cells

9
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 divisionsMeiosis I
  and Meiosis II

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figure 09-14a.jpg
figure 09-14a.jpg
Synapsis
Synapsis
Figure 9.14 Part 1
Figure 9.14 Part 1
Figure 9.14 Part 1
Figure 9.14 Part 1
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figure 09-16.jpg
Figure 9.16
Figure 9.16
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figure 09-14b.jpg
Figure 9.14 Part 2
Figure 9.14 Part 2
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Meiosis A Pair of Nuclear Divisions

• Prophase I A) homologous chromosomes pair, B)
  material may be exchanged by crossing over
  between nonsister chromatids of two homologous
  chromosomes.
• Metaphase I the paired homologs gather at the
  equatorial plate.
• Anaphase I entire chromosomes, each with two
  chromatids, migrate to the poles.
• Telophase I two nuclei, each with the haploid
  number of chromosomes with two sister chromatids.
  Review Figures 9.14, 9.16

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Meiosis A Pair of Nuclear Divisions

• Intephase II No DNA Replication
• Meiosis II sister chromatids separate.
• The result of meiosis is four cells, each with a
  haploid chromosome content, and genetic
  uniqueness.

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figure 09-17a.jpg
Figure 9.17 Part 1
Figure 9.17 Part 1
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figure 09-17b.jpg
Figure 9.17 Part 2
Figure 9.17 Part 2
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Meiosis A Pair of Nuclear Divisions

• Both crossing over during prophase I and the
  random selection of which homolog of a pair
  migrates to which pole during anaphase I ensure
  that the genetic composition of each haploid
  gamete is different from that of the parent and
  from that of the other gametes. The more
  chromosome pairs there are in a diploid cell, the
  greater the diversity of chromosome combinations
  generated by meiosis.