Henrietta Lacks' immortal HeLa cells are used widely in medical research to study cancer, viruses, and other cell processes. Cells reproduce through mitosis, which duplicates DNA and divides the cell into two identical daughter cells. Mitosis maintains the chromosome number while meiosis halves it, producing gametes for sexual reproduction. Meiosis involves two nuclear divisions, mixing parental chromosomes and alleles in offspring.

1. BIOLOGY: Today and Tomorrow, 4e
starr evers starr
Chapter 8
How Cells Reproduce

2. 8.1 Henrietta’s Immortal Cells
 Henrietta Lacks died of cervical cancer more than 50 years
ago, but her cells live on in research laboratories
 HeLa cells are widely used to investigate cancer, viral growth,
protein synthesis, effects of radiation, and many other
processes important in medicine and research
 Understanding why cancer cells are immortal – and we are
not – begins with understanding the structures and
mechanisms that cells use to divide

3. Dividing HeLa Cells

4. 8.2 Multiplication by Division
 A cell reproduces by dividing in two
 Each descendant cell receives a full set of chromosomes and
some cytoplasm
 Before the cell’s cytoplasm divides, it must first replicate its
chromosomes
 Duplicated chromosomes are separated and packaged into
new nuclei by one of two mechanisms: mitosis or meiosis

5. Mitosis and Meiosis
 Mitosis is a nuclear division mechanism that maintains the
chromosome – used in growth, development, replacement of
damaged or dead cells, or as part of asexual reproduction
 Meiosis is a nuclear division mechanism that halves the
chromosome number – used in sexual reproduction, in
which two parents contribute genes to offspring

6. Divisions of a Fertilized Frog Egg

7. Cellular Division Mechanisms

8. 8.3 Mitosis and the Cell Cycle
 Cell cycle
 A series of events from the time a cell forms until its
cytoplasm divides
 Includes three phases: interphase, mitosis, and
cytoplasmic division

9. Interphase
 Most of a cell’s activities occur in interphase
 Interphase
 In a eukaryotic cell cycle, the interval between mitotic
divisions when a cell grows, roughly doubles the number
of its cytoplasmic components, and replicates its DNA
 Three stages:
 G1, 1st interval (gap) of growth before DNA replication
 S, interval of synthesis (DNA replication)
 G2, 2nd interval (gap) when the cell prepares to divide

10. The eukaryotic cell cycle

11. Controls Over the Cell Cycle
 When a cell divides—and when it does not—is determined by
gene expression controls
 Products of “checkpoint genes” monitor whether a cell’s
DNA has been copied completely, whether it is damaged, and
whether enough nutrients are available
 If a problem remains uncorrected, other checkpoint proteins
may cause the cell to self-destruct

12. Homologous Chromosomes
 Human body cells have 23 chromosome pairs
 Except for a pairing of sex chromosomes (XY) in males, the
chromosomes of each pair are homologous
 Homologous chromosomes are members of a pair of
chromosomes with the same length, shape, and genes
 One member of a homologous pair was inherited from the
female parent, and the other from the male parent

13. How Mitosis Maintains Chromosome Number
 Mitosis distributes a complete set of chromosomes into two
new nuclei
 In G2, each chromosomes consists of two replicated DNA
molecules attached at the centromere (sister chromatids)
 When sister chromatids are pulled apart, each becomes an
individual chromosome in a new nucleus
 When the cytoplasm divides, the two nuclei are packaged into
two separate cells

14. How Mitosis Maintains Chromosome Number
A) An unduplicated
pair of chromosomes
in a cell in G1.
B) By G2, each
chromosome has been
duplicated.
C) Mitosis and cytoplasmic
division package one copy of
each chromosome into each
of two new cells.

15. Figure 8-4 p135
A) An unduplicated
pair of chromosomes
in a cell in G1.
Stepped Art
B) By G2, each
chromosome has
been duplicated.
C) Mitosis and
cytoplasmic division
package one copy of each
chromosome into each of
two new cells.

16. The Process of Mitosis
 Prophase
 Chromosomes condense and spindle forms
 Nuclear envelope breaks up
 Spindle microtubules attach to chromosomes
 Spindle
 Moves chromosomes during nuclear division
 Dynamically assembled and disassembled microtubules

17. The Process of Mitosis
 Metaphase
 Duplicated homologous chromosomes line up at the
spindle equator (halfway between spindle poles)
 Sister chromatids begin to move apart toward opposite
spindle poles
 Anaphase
 Microtubules separate sister chromatids of each
chromosome and pull them toward opposite spindle poles
 Each DNA molecule is now a separate chromosome

18. The Process of Mitosis
 Telophase
 Two clusters of chromosomes arrive at the spindle poles
and decondense; new nuclei form
 End of mitosis
 Nuclear envelopes form around the two clusters of
chromosomes, forming two new nuclei with the parental
chromosome number

19. Mitosis in a plant cell Mitosis in an animal cell
pair of
centrioles
1 Interphase
Interphase cells are shown for comparison, but interphase is not part of mitosis.
The red spots in the plant cell nucleus are areas where ribosome subunits are
being transcribed and assembled.
Mitosis

20. Mitosis in a plant cell Mitosis in an animal cell
2 Early prophase
Mitosis begins. Transcription stops, and the DNA begins to appear grainy as it
starts to condense. The centriole pair gets duplicated.
Mitosis

21. Mitosis in a plant cell Mitosis in an animal cell
microtubule of spindle
3 Prophase
The duplicated chromosomes become visible as they condense. One of the two
centriole pairs moves to the opposite side of the cell. The nuclear envelope
breaks up. Spindle microtubules assemble and bind to chromosomes at the
centromere. Sister chromatids become attached to opposite centriole pairs.
Mitosis

22. Mitosis in a plant cell Mitosis in an animal cell
4 Metaphase
All of the chromosomes are aligned in the middle of the cell.
Mitosis

23. Mitosis in a plant cell Mitosis in an animal cell
5 Anaphase
Spindle microtubules separate the sister chromatids and move them toward
opposite sides of the cell. Each sister chromatid has now become an individual,
unduplicated chromosome.
Mitosis

24. Mitosis in a plant cell Mitosis in an animal cell
6 Telophase
The chromosomes reach opposite sides of the cell and decondense. Mitosis ends
when a new nuclear envelope forms around each cluster of chromosomes.
Mitosis

25. ANIMATED FIGURE: Random alignment
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26. ANIMATED FIGURE: The cell cycle
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27. 3D ANIMATION: Mitosis

28. 8.4 Cytoplasmic Division Mechanisms
 A cell’s cytoplasm divides between late anaphase and the
end of telophase, forming two cells, each with its own nucleus
 Mechanisms of cytoplasmic division differ between animal
cells and plant cells

29. Cytoplasmic Division in Animal Cells
 In animal cells, a contractile ring pinches the cytoplasm in two
 A contractile ring of microfilaments contracts when its
component proteins are energized by ATP
 The cleavage furrow produced deepens until the cytoplasm
(and the cell) is pinched in two
 Each new cell has its own nucleus, cytoplasm, and is
enclosed by a plasma membrane

30. Cytoplasmic Division of an Animal Cell

31. Cytoplasmic Division in Plant Cells
 In plant cells, microtubules guide vesicles from Golgi bodies
and the cell surface to the division plane
 Vesicles and their wall-building contents fuse into a disk-
shaped cell plate
 The cell plate grows and forms a cross-wall between the two
new nuclei
 The cell plate develops into two new cell walls, separating the
descendant cells

32. Cytoplasmic Division of a Plant Cell

33. ANIMATED FIGURE: Cytoplasmic division
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34. 8.5 When Mitosis Becomes Pathological
 When checkpoint mechanisms fail, the cell may skip
interphase and keep dividing with no resting period
 Signaling mechanisms that make an abnormal cell die may
stop working
 Mutations are passed along to the cell’s descendants, which
form a neoplasm, an accumulation of cells that lost control
over how they grow and divide

35. Tumors and Oncogenes
 A neoplasm that forms a lump is a tumor
 An oncogene is any gene that helps transform a normal cell
into a tumor cell
 Genes for proteins that promote mitosis are called proto-
oncogenes because mutations can turn them into oncogenes
 Example: Genes that code for receptors for growth factors

36. An oncogene causing a neoplasm

37. Tumor Suppressors
 Checkpoint gene products that inhibit mitosis are called tumor
suppressors because tumors form when they are missing
 Example: Products of BRCA1 and BRCA2 genes
 Viruses such as HPV cause a cell to make proteins that
interfere with its own tumor suppressors

38. Checkpoint genes control cell division

39. Cancer
 A benign neoplasm such as a mole is noncancerous; a
malignant neoplasm is dangerous to health
 Cancer occurs when abnormally dividing cells of a malignant
neoplasm disrupt body tissues, physically and metabolically
 Malignant neoplasms can break free and invade other tissues
(metastasis)

40. Metastasis
Benign neoplasms
grow slowly and stay
in their home tissue.
Cells of a malignant
neoplasm can break away
from their home tissue.
Malignant cells can become attached to the wall
of a blood vessel or lymph vessel. They release
enzymes that create an opening in the wall, then
enter the vessel.
The cells creep or tumble along in blood vessels,
then leave the bloodstream the same way they got
in. They may start growing in other tissues, a
process called metastasis.
1
4
3
2

41. Three Characteristics of Cancer Cells
1. Grow and divide abnormally
2. Abnormal plasma membrane, cytoskeleton, chromosome
number, and metabolism
3. Cells do not stay anchored properly in tissues because
plasma membrane adhesion proteins are defective or missing

42. Detecting Skin Cancer
C) Melanoma, a malignant
neoplasm of skin cells, spreads
fastest. Cells form
dark, encrusted lumps that may
itch or bleed easily.
B) The second most common
form of skin cancer is a
squamous cell carcinoma.
This pink growth, firm to the
touch, grows under the surface
of skin.
A) Basal cell carcinoma is the
most common type of skin
cancer. This slow growing,
raised lump may be
uncolored, reddish brown, or
black.

43. ANIMATED FIGURE: Cancer and metastasis
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44. VIDEO: Genome Research Improving Cancer
Understanding

45. VIDEO: The War on Cancer

46. VIDEO: Genetically Modified Virus Used to Fight
Cancer

47. 8.6 Sex and Alleles
 Asexual reproduction
 Offspring arise from one parent
 Offspring are genetic clones
 Sexual reproduction
 Offspring inherit genes from two parents
 Diversity offers a better chance of surviving an
environmental challenge or harmful mutations
 Beneficial mutations spread quickly

48. Introducing Alleles
 Paired genes on homologous chromosomes often vary
slightly in DNA sequence
 Alleles are forms of a gene that encode slightly different
versions of the gene’s product
 Offspring of sexual reproducers inherit new combinations of
alleles, which is the basis of new combinations of traits

49. A) Corresponding colored patches in this
fluorescence micrograph indicate
corresponding DNA sequences in
a homologous chromosome pair. These
chromosomes carry the same set of genes.
Alleles

50. Genes occur in pairs on
homologous
chromosomes.
The members of each
pair of genes may be
identical, or they may
differ slightly, as alleles.
B) Homologous chromosomes carry the
same series of genes, but the DNA
sequence of any one of those genes
might differ just a bit from that of its
partner on the homologous chromosome.
Alleles

51. ANIMATED FIGURE: Genetic terms
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52. 8.7 Meiosis and the Life Cycle
 Meiosis halves the parental chromosome number by sorting
the chromosomes into new nuclei twice (meiosis I and
meiosis II)
 Duplicated chromosomes of a diploid nucleus (2n) are
distributed into four haploid nuclei (n)

53. Two Stages of Meiosis

54. Meiosis
 Meiosis I
 In the first nuclear division, duplicated homologous
chromosomes line up and cross over, then move apart,
toward opposite spindle poles
 Two new nuclear envelopes form around the two clusters
of still-duplicated chromosomes
 Meiosis II
 The second nuclear division separates sister chromatids
 Four haploid nuclei typically form, each with one complete
set of unduplicated chromosomes

55. Meiosis I One diploid nucleus to two haploid nuclei
1 2 3 4Prophase I Metaphase I Anaphase I Telophase I
plasma
membrane
spindle
nuclear
envelope breaking up
centiole pair one pair of
homologous chromosomes
Meiosis

56. No DNA
replication
Meiosis II Two haploid nuclei to four haploid nuclei
5 6 7 8Prophase II Metaphase II Anaphase II Telophase II
Meiosis

57. Meiosis Mixes Alleles
 Meiosis shuffles parental combinations of alleles, introducing
variation in offspring
 Crossing over in prophase I
 Random assortment in metaphase I
 Crossing over is recombination between nonsister
chromatids of homologous chromosomes which produces
new combinations of parental alleles

58. A) Here, we focus on only two of the many genes on a chromosome. In this example, one
gene has alleles A and a; the other has alleles B and b.
Crossing Over

59. crossover
B) Close contact between homologous chromosomes promotes crossing over between
nonsister chromatids, which exchange corresponding pieces.
Crossing Over

60. C) Crossing over mixes up paternal and maternal alleles on homologous chromosomes.
Crossing Over

61. From Gametes to Offspring
 Sexual reproduction involves the fusion of reproductive cells
(gametes) from two parents
 All gametes are haploid, and they arise by division of
immature reproductive cells (germ cells)
 At fertilization, two haploid gametes fuse and produce a
diploid zygote, which is the first cell of a new individual

62. Gametes in Animals and Plants
 In animals, meiosis of germ cells in the reproductive organs
give rise to sperm (male gametes) or eggs (female gametes)
 In plants, two kinds of multicelled bodies form:
 A diploid sporophyte produces spores by meiosis
 Gametes form in a haploid gametophyte

63. mitosis
zygote (2n)
multicelled body
(2n)
Diploid
Fertilization
Haploid
Meiosis
gametes (n)
A) Generalized life cycle for most animals.
Generalized life cycle
for animals

64. mitosis
zygote (2n)
multicelled sporophyte
(2n)
Diploid
Fertilization
Haploid
Meiosis
gametes (n) spores (n)
multicelled
gametophyte (n)
B) Generalized life cycle for most plants.
Generalized life cycle
for plants

65. ANIMATED FIGURE: Crossing over
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66. ANIMATED FIGURE: Generalized life cycles
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67. ANIMATION: Meiosis I and II
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68. 3D ANIMATION: Meiosis

69. ANIMATION: Crossover review
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70. ANIMATION: Stages of Mitosis and Meiosis
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71. ANIMATION:
Meiosis and Mitosis Drag and Drop
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72. 8.8 Henrietta’s Immortal Cells (revisited)
 HeLa cells were used in early tests of taxol, a drug that keeps
microtubules from disassembling and interferes with mitosis
 The HeLa cell line was established more than 50 years ago
without Henrietta Lacks knowledge or consent
 Today, consent forms are required to take tissue samples

73. Digging Into Data:
HeLa Cells Are a Genetic Mess