1. CHAPTER 9 Chromosomes, the Cell Cycle, and Cell Division

2. 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

3. 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

4. Cell Division
Cell division is necessary for reproduction, growth, and repair of an organism. 4

5. 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 5

6. Systems of Cell Reproduction
In prokaryotes, cellular DNA is a single molecule, or chromosome.
Prokaryotes reproduce by cell fission.
Review Figure 9.3 6

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Figure 9.3
Figure 9.3

8. Systems of Cell Reproduction
In eukaryotes, nuclei divide by either mitosis or meiosis. 8

9. Interphase and the Control of Cell Division
The mitotic cell cycle has two main phases: interphase and mitosis. 9

10. 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 10

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Figure 9.4
Figure 9.4

12. 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 12

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Figure 9.5
Figure 9.5

14. 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. 14

15. 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. 15

16. 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 16

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Figure 9.7
Figure 9.7

18. 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 18

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Figure 9.9
Figure 9.9

20. Mitosis: Distributing Exact Copies of Genetic Information
Mitosis can be divided into phases:
prophase
metaphase
anaphase
telophase
Review Figure 9.8 20

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Figure 9.8 – Part 1
Figure 9.8 – Part 1

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Figure 9.8 – Part 2
Figure 9.8 – Part 2

23. 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. 23

24. 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. 24

25. 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 25

26. 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. 26

27. Reproduction: Sexual and Asexual
Asexual reproduction produces an organism genetically identical to the parent.
Any genetic variety is the result of mutations. 28

28. Reproduction: Sexual and Asexual
In sexual reproduction, two haploid gametes—one from each parent—unite in fertilization to form a genetically unique, diploid zygote.
Review Figure 9.12 29

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Figure 9.12 – Part 1
Figure 9.12 – Part 1

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Figure 9.12 – Part 2
Figure 9.12 – Part 2

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Figure 9.12 – Part 3
Figure 9.12 – Part 3

32. 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. 33

33. Reproduction: Sexual and Asexual
The number, shapes, and sizes of the chromosomes constitute the karyotype of an organism. 34

34. 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 35

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Figure 9.14 – Part 1
Figure 9.14 – Part 1

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Figure 9.14 – Part 2
Figure 9.14 – Part 2

37. 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 38

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Figure 9.16
Figure 9.16

39. 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 40

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Figure 9.17 – Part 1
Figure 9.17 – Part 1

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Figure 9.17 – Part 2
Figure 9.17 – Part 2

42. 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. 43

43. 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 44

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Figure 9.18
Figure 9.18

45. 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 46

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Figure 9.19
Figure 9.19