1. Chromosomes, Mitosis and Meiosis
Chapter 10

2. Learning Objective 1
What is the significance of chromosomes in terms of information?

3. Chromosomes

4. Organization Genes Chromatin Chromosomes cell’s informational units
made of DNA
Chromatin
DNA and protein
makes up chromosomes (eukaryotes)
Chromosomes
allow DNA sorting
into daughter cells

5. KEY CONCEPTS
In eukaryotic cells, DNA is wound around specific proteins to form chromatin, which in turn is folded and packaged to make individual chromosomes

6. Learning Objective 2
How is DNA organized in prokaryotic and eukaryotic cells?

7. Prokaryotic Cells
Contain circular DNA molecules

8. Eukaryotic Chromosomes
Nucleosome
histone (protein) bead wrapped in DNA
organized into coiled loops
held together by nonhistone scaffolding proteins

9. Nucleosomes

10. DNA wound around a cluster of histone molecules Histone tails
Linker DNA
Figure 10.2: Nucleosomes.
Nucleosome
(10 nm diameter)
Fig. 10-2a, p. 213

11. Figure 10.2: Nucleosomes.
100 nm
Fig. 10-2b, p. 213

12. Scaffolding Proteins

13. DNA Scaffolding proteins 2 μm Fig. 10-3, p. 213
Figure 10.3: TEM of a mouse chromosome depleted of histones.
Notice how densely packed the DNA strands are, even though they have been released from the histone proteins that organize them into tightly coiled structures.
2 μm
Fig. 10-3, p. 213

14. Chromosome Organization

15. Condensed chromatin Extended chromatin
1400 nm
700 nm
300 nm fiber (looped domains)
30 nm chromatin fiber
DNA wound around a cluster of histone molecules
Scaffolding protein
Condensed chromosome
Condensed chromatin
Extended
chromatin
Packed nucleosomes
Figure 10.4: Organization of a eukaryotic chromosome.
This diagram shows how DNA is packaged into highly condensed chromosomes. First, DNA is wrapped around histone proteins to form nucleosomes. Then, the nucleosomes are compacted into chromatin fibers, which are coiled into looped domains. The looped domains are compacted, ultimately forming chromosomes.
Histone
10 nm
Nucleosomes
2 nm
DNA double helix
Fig. 10-4, p. 214

16. Learning Objective 3
What are the stages in the eukaryotic cell cycle, and their principal events?

17. Eukaryotic Cell Cycle
Cycle of cell division
interphase
M phase

18. (Mitosis and cytokinesis)
INTERPHASE G1
(First gap phase) S
(Synthesis phase) G2
(Second gap phase)
Figure 10.5: The eukaryotic cell cycle.
The cell cycle includes interphase (G1, S, and G2) and M phase (mitosis and cytokinesis). Proportionate amounts of time spent at each stage vary among species, cell types, and growth conditions. If the cell cycle were a period of 12 hours, G1 would be about 5 hours, S would be 4.5 hours, G2 would be 2 hours, and M phase would be 30 minutes.
M PHASE
(Mitosis and cytokinesis)
Fig. 10-5, p. 215

19. Interphase First gap phase (G1 phase) Synthesis phase (S phase)
cell grows and prepares for S phase
Synthesis phase (S phase)
DNA and chromosome protein synthesis
chromosome duplication
Second gap phase (G2 phase)
protein synthesis increases
preparation for cell division

20. M Phase Mitosis Cytokinesis nuclear division
two nuclei identical to parent nucleus
Cytokinesis
cytoplasm divides
two daughter cells

21. KEY CONCEPTS
Cell division is an important part of the cell cycle, which consists of the successive stages through which a cell passes

22. Animation: The Cell Cycle
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23. Learning Objective 4
What is the structure of a duplicated chromosome, including the sister chromatids, centromeres, and kinetochores?

24. A Duplicated Chromosome
Consists of a pair of sister chromatids
containing identical DNA sequences
Centromere
constricted region
joins sister chromatids
Kinetochore
protein to which microtubules bind
attached to centromere

25. Sister Chromatids

26. Centromere region Microtubules Kinetochore Sister chromatids 1.0 μm
Figure 10.7: Sister chromatids and centromeres.
The sister chromatids, each consisting of tightly coiled chromatin fibers, are tightly associated at their centromere regions, indicated by the brackets. Associated with each centromere is a kinetochore, which serves as a microtubule attachment site. Kinetochores and microtubules are not visible in this TEM of a metaphase chromosome.
Kinetochore
Sister chromatids
1.0 μm
Fig. 10-7, p. 218

27. Learning Objective 5
What is the process and significance of mitosis?

28. Mitosis Preserves chromosome number
in eukaryotic cell division
Identical chromosomes are distributed to each pole of the cell
nuclear envelope forms around each set

29. Interphase

30. Sister chromatids of duplicated chromosome Kinetochore Chromatin
INTERPHASE
PROPHASE
PROMETAPHASE
Nucleolus
Sister chromatids of duplicated chromosome
Kinetochore
Chromatin
Nucleus
Pieces of nuclear envelope
Spindle microtubule
Figure 10.6: Interphase and the stages of mitosis.
The LMs show plant cells, which lack centrioles. The drawings depict generalized animal cells with a diploid chromosome number of 4; the sizes of the nuclei and chromosomes are exaggerated to show the structures more clearly.
Nuclear envelope
Centrioles
Developing mitotic spindle
Plasma membrane
Fig. 10-6a, p. 216

31. Prophase
Chromatin condenses into duplicated chromosomes (pair of sister chromatids)
Nuclear envelope begins to disappear
Mitotic spindle begins to form

32. Mitotic Spindle

33. Metaphase plate (cell’s midplane)
Kinetochore microtubule (spindle microtubule)
Centrioles
Astral microtubules
Pericentriolar material
Figure 10.9: The mitotic spindle.
Polar (non- kinetochore) microtubule
Sister chromatids
Fig. 10-9a, p. 219

34. Figure 10.9: The mitotic spindle.
Fig. 10-9b, p. 219

35. Prophase

36. Prometaphase
Spindle microtubules attach to kinetochores of chromosomes
Chromosomes begin to move toward cell’s midplane

37. Prometaphase

38. Metaphase Chromosomes align on cell’s midplane (metaphase plate)
Mitotic spindle is complete
Microtubules attach kinetochores of sister chromatids to opposite poles of cell

39. Metaphase

40. Anaphase Sister chromatids separate
move to opposite poles
Each former chromatid is now a chromosome

41. Anaphase

42. Telophase Nuclear envelope re-forms Nucleoli appear Chromosomes uncoil
Spindle disappears
Cytokinesis begins

43. Telophase

44. Reforming nuclear envelope
METAPHASE
ANAPHASE
TELOPHASE
25 μm
Spindle
Cleavage furrow
Centriole pair at spindle pole
Figure 10.6: Interphase and the stages of mitosis.
The LMs show plant cells, which lack centrioles. The drawings depict generalized animal cells with a diploid chromosome number of 4; the sizes of the nuclei and chromosomes are exaggerated to show the structures more clearly.
Reforming nuclear envelope
Daughter chromosomes
Cell’s midplane (metaphase plate)
Fig. 10-6b, p. 217

45. KEY CONCEPTS
In cell division by mitosis, duplicated chromosomes separate (split apart) and are evenly distributed into two daughter nuclei

46. Cytokinesis

47. Actomyosin contractile ring
Cleavage furrow
Actomyosin contractile ring
Figure 10.10: Cytokinesis in animal and plant cells.
The nuclei in both TEMs are in telophase. The drawings show 3-D relationships.
10 μm
Fig a, p. 220

48. Small vesicles fuse, forming larger vesicles Cell plate forming
Nucleus
Vesicles gather on cell’s midplane
Eventually one large vesicle exists
New cell walls (from vesicle contents)
Plasma membrane
Figure 10.10: Cytokinesis in animal and plant cells.
The nuclei in both TEMs are in telophase. The drawings show 3-D relationships.
Cell wall
Cell plate forming
New plasma membranes (from vesicle membranes)
5 μm
Fig b, p. 220

49. Learning Objective 6
How is the cell cycle controlled?

50. Cell-Cycle Control Cyclin-dependent kinases (Cdks) Cyclins
protein kinases that control cell cycle
active only when bound to cyclins
Cyclins
regulatory proteins
levels fluctuate during cell cycle

51. Cyclins

52. M-Cdk (triggers M phase)1 1 1
Cyclin is synthesized and accumulates. 2 2
Cdk associates with cyclin, forming a cyclin–Cdk complex, M-Cdk. 3 3
M-Cdk phosphorylates proteins, activating those that facilitate mitosis and inactivating those that inhibit mitosis.
Cdk 5 G1 S 4 4
An activated enzyme complex recognizes a specific amino acid sequence in cyclin and targets it for destruction. When cyclin is degraded, M-Cdk activity is terminated, and the cells formed by mitosis enter G1. M G2 5
Cyclin 5
Cdk is not degraded but is recycled and reused.
Figure 10.12: Molecular control of the cell cycle.
This diagram is a simplified view of the control system that triggers the cell to move from G2 to M phase. 2 4
Degraded cyclin
Cdk
M-Cdk (triggers M phase) 3
Fig , p. 222

53. KEY CONCEPTS
An internal genetic program interacts with external signals to regulate the cell cycle

54. Learning Objective 7
What is the difference between asexual and sexual reproduction?

55. Asexual Reproduction Single parent Mitosis
offspring have identical hereditary traits
Mitosis
basis for eukaryotic asexual reproduction

56. Binary Fission

57. DNA replication begins at single site on bacterial DNA. Bacterial DNA
Prokaryotic cell
Plasma membrane 1
DNA replication begins at single site on bacterial DNA.
Bacterial DNA
Cell wall
Origin of replication 2
Replication continues, as replication enzymes work in both directions from site where replication began.
Two copies of bacterial DNA 3
Replication is completed. Cell begins to divide, as plasma membrane grows inward.
Figure 10.11: Most prokaryotes reproduce by binary fission.
The circular DNA molecule is much longer than depicted here. 4
Binary fission is complete. Two identical prokaryotic cells result.
Two identical prokaryotic cells
Fig , p. 221

58. Sexual Reproduction
Two haploid sex cells (gametes) fuse to form a single diploid zygote
Meiosis
produces gametes

59. Learning Objective 8
What is the difference between haploid and diploid cells?
What are homologous chromosomes?

60. Diploid Cell Chromosomes are paired (homologous chromosomes)
similar in length, shape, other features
carry genes affecting the same traits

61. Haploid Cell
Contains only one member of each homologous chromosome pair

62. Fig. 10-16, p. 229 Figure 10.16: Mitosis and meiosis.
This drawing compares the events and outcomes of mitosis and meiosis, in each case beginning with a diploid cell with four chromosomes (two pairs of homologous chromosomes). Because the chromosomes duplicated in the previous interphase, each chromosome consists of two sister chromatids. The chromosomes derived from one parent are shown in blue, and those from the other parent are red. Homologous pairs are similar in size and shape. Chiasmata are not shown, and some of the stages have been omitted for simplicity.
Fig , p. 229

63. No synapsis of homologous chromosomes
MITOSIS
PROPHASE
No synapsis of homologous chromosomes
ANAPHASE
Sister chromatids move to opposite poles
Figure 10.16: Mitosis and meiosis.
This drawing compares the events and outcomes of mitosis and meiosis, in each case beginning with a diploid cell with four chromosomes (two pairs of homologous chromosomes). Because the chromosomes duplicated in the previous interphase, each chromosome consists of two sister chromatids. The chromosomes derived from one parent are shown in blue, and those from the other parent are red. Homologous pairs are similar in size and shape. Chiasmata are not shown, and some of the stages have been omitted for simplicity.
DAUGHTER CELLS
Two 2n cells with unduplicated chromosomes
Fig a, p. 229

64. Synapsis of homologous chromosomes to form tetrads
MEIOSIS
PROPHASE I
Synapsis of homologous chromosomes to form tetrads
ANAPHASE I
Homologous chromosomes move to opposite poles
PROPHASE II
Two n cells with duplicated chromosomes
Figure 10.16: Mitosis and meiosis.
This drawing compares the events and outcomes of mitosis and meiosis, in each case beginning with a diploid cell with four chromosomes (two pairs of homologous chromosomes). Because the chromosomes duplicated in the previous interphase, each chromosome consists of two sister chromatids. The chromosomes derived from one parent are shown in blue, and those from the other parent are red. Homologous pairs are similar in size and shape. Chiasmata are not shown, and some of the stages have been omitted for simplicity.
ANAPHASE II
Sister chromatids move to opposite poles
HAPLOID CELLS
Four n cells with unduplicated chromosomes
Fig b, p. 229

65. Learning Objective 9
What is the process and significance of meiosis?

66. Meiosis
One diploid cell divides two times, yielding four haploid cells
Sexual life cycles in eukaryotes require meiosis
each gamete contains half the number of chromosomes in parent cell

67. Meiosis I Prophase I Crossing-over Results in genetic recombination
homologous chromosomes join (synapsis)
Crossing-over
between homologous (nonsister) chromatids
exchanges segments of DNA strands
Results in genetic recombination

68. Synapsis

69. Maternal sister chromatids
Paternal sister chromatids
Synaptonemal complex
Figure 10.14: A synaptonemal complex.
Synapsing homologous chromosomes in meiotic prophase I are held together by a synaptonemal complex, composed mainly of protein.
Chromatin
Protein
Chromatin
Maternal sister chromatids
Fig a, p. 228

70. Chromosome Chromosome Synaptonemal complex 0.5 μm Fig. 10-14b, p. 228
Figure 10.14: A synaptonemal complex.
Synapsing homologous chromosomes in meiotic prophase I are held together by a synaptonemal complex, composed mainly of protein.
Chromosome
0.5 μm
Fig b, p. 228

71. Meiosis I Metaphase I Anaphase I
tetrads (homologous chromosomes joined by chiasmata) line up on metaphase plate
Anaphase I
homologous chromosomes separate
distributed to different nuclei
Each nucleus contains haploid number of chromosomes
each chromosome has 2 chromatids

72. Tetrads and Chiasmata

73. Sister chromatids Chiasmata Kinetochores Sister chromatids 1 μm
Figure 10.15: A meiotic tetrad with two chiasmata.
The two chiasmata are the result of separate crossing-over events.
1 μm
Fig a, p. 228

74. Sister chromatids Chiasmata Kinetochores Fig. 10-15b, p. 228
Figure 10.15: A meiotic tetrad with two chiasmata.
The two chiasmata are the result of separate crossing-over events.
Fig b, p. 228

75. Meiosis II Two chromatids of each chromosome separate
one distributed to each daughter cell
Each former chromatid is now a chromosome

76. Meiosis

77. Meiosis

78. Homologous chromosomes Chromatin
INTERPHASE
MEIOSIS I
Mid-prophase I
Late prophase I
Nucleolus
Nuclear envelope
Homologous chromosomes
Chromatin
Figure 10.13: Interphase and the stages of meiosis.
Meiosis consists of two nuclear divisions, meiosis I (top row) and meiosis II (bottom row). The LMs show sectioned plant cells, which lack centrioles. The drawings depict generalized animal cells with a diploid chromosome number of 4; the sizes of the nuclei and chromosomes are exaggerated to show the structures more clearly.
Developing meiotic spindle
Centrioles
Interphase preceding meiosis; DNA replicates.
Homologous chromosomes synapse, forming tetrads; nuclear envelope breaks down.
Fig a (1), p. 226

79. Chromosomes line up along cell's midplane.
MEIOSIS II
Prophase II
Metaphase II
Anaphase II
Daughter chromosomes
Figure 10.13: Interphase and the stages of meiosis.
Meiosis consists of two nuclear divisions, meiosis I (top row) and meiosis II (bottom row). The LMs show sectioned plant cells, which lack centrioles. The drawings depict generalized animal cells with a diploid chromosome number of 4; the sizes of the nuclei and chromosomes are exaggerated to show the structures more clearly.
Chromosomes condense again following brief period of interkinesis. DNA does not replicate again.
Chromosomes line up along cell's midplane.
Sister chromatids separate, and chromosomes move to opposite poles.
Fig a (2), p. 226

80. Microtubule attached to kinetochore Cleavage furrow
Metaphase I
Anaphase I
Telophase I
Microtubule attached to kinetochore
Cleavage furrow
Separation of homologous chromosomes
Figure 10.13: Interphase and the stages of meiosis.
Meiosis consists of two nuclear divisions, meiosis I (top row) and meiosis II (bottom row). The LMs show sectioned plant cells, which lack centrioles. The drawings depict generalized animal cells with a diploid chromosome number of 4; the sizes of the nuclei and chromosomes are exaggerated to show the structures more clearly.
Sister chromatids
Tetrads line up on cell's midplane. Tetrads held together at chiasmata (sites of prior crossing-over).
Homologous chromosomes separate and move to opposite poles. Note that sister chromatids remain attached at their centromeres.
One of each pair of homologous chromosomes is at each pole. Cytokinesis occurs.
Fig b (1), p. 227

81. Nuclei form at opposite poles of each cell. Cytokinesis occurs.
Telophase II
Four haploid cells
25 μm
Figure 10.13: Interphase and the stages of meiosis.
Meiosis consists of two nuclear divisions, meiosis I (top row) and meiosis II (bottom row). The LMs show sectioned plant cells, which lack centrioles. The drawings depict generalized animal cells with a diploid chromosome number of 4; the sizes of the nuclei and chromosomes are exaggerated to show the structures more clearly.
Nuclei form at opposite poles of each cell. Cytokinesis occurs.
Four gametes (animal) or four spores (plant) are produced.
Fig b (2), p. 227

82. Learning Objective 10
What are the different processes and outcomes of mitosis and meiosis?

83. Mitosis Single nuclear division
2 daughter cells genetically identical to each other and to original cell
No synapsis of homologous chromosomes

84. Mitosis

85. Meiosis Two successive nuclear divisions form four haploid cells
Synapsis of homologous chromosomes occurs during prophase I

86. Meiosis

87. KEY CONCEPTS
Meiosis, which reduces the number of chromosome sets from diploid to haploid, is necessary to maintain the normal chromosome number when two cells join during sexual reproduction

88. KEY CONCEPTS
Meiosis helps to increase genetic variation among offspring

89. Learning Objective 11
Compare the roles of mitosis and meiosis in various generalized life cycles

90. Animals Somatic cells are diploid Gametes are haploid
produced by mitosis
Gametes are haploid
produced by meiosis (gametogenesis)

91. Animal Life Cycle

92. Multicellular diploid organism (2n)
Gametes (n)
Meiosis
Fertilization
Zygote (2n)
Mitosis
Figure 10.17: Representative life cycles.
The color code and design here is used throughout the rest of the book. For example, in all life cycles the haploid (n) generation is shown in purple, and the diploid (2n) generation is gold. The processes of meiosis and fertilization always link the haploid and diploid generations.
Multicellular diploid organism (2n)
Animals
Fig a, p. 230

93. Simple Eukaryotes May be haploid Only diploid stage is the zygote
produced by mitosis
Only diploid stage is the zygote
which undergoes meiosis to restore the haploid state

94. Simple Eukaryote Life Cycle

95. Unicellular or multicellular haploid organism (n)
Mitosis
Mitosis
Gametes (n)
Figure 10.17: Representative life cycles.
The color code and design here is used throughout the rest of the book. For example, in all life cycles the haploid (n) generation is shown in purple, and the diploid (2n) generation is gold. The processes of meiosis and fertilization always link the haploid and diploid generations.
Meiosis
Fertilization
Zygote (2n)
Simple eukaryotes
Fig b, p. 230

96. Plants Alternation of generations: sporophyte generation
gametophyte generation

97. Plants Sporophyte generation
multicellular diploid
forms haploid spores by meiosis
Spore divides (mitosis) to form gametophyte generation
multicellular haploid
produces gametes by mitosis

98. Plants Two haploid gametes fuse to form diploid zygote
Zygote divides (mitosis) to produce new diploid sporophyte generation

99. Plant Life Cycle

100. Gametophyte (n) (multicellular haploid organism)
Mitosis
Mitosis
Spores (n)
Gametes (n)
Meiosis
Fertilization
Zygote (2n)
Figure 10.17: Representative life cycles.
The color code and design here is used throughout the rest of the book. For example, in all life cycles the haploid (n) generation is shown in purple, and the diploid (2n) generation is gold. The processes of meiosis and fertilization always link the haploid and diploid generations.
Mitosis
Sporophyte (2n) (multicellular diploid organism)
Plants, some algae, and some fungi
Fig c, p. 230

101. Animation: Cancer and Metastasis
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