1. CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION
8.1 Like begets like, more or less
Asexual reproduction
Chromosomes are duplicated and cell divides
Each daughter cell is genetically identical to the parent and the other daughter
Sexual reproduction
Each offspring inherits a unique combination of genes from both parents
Offspring can show great variation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

3. 8.2 Cells arise only from preexisting cells
"Every cell from a cell" is at the heart of the perpetuation of life
Can reproduce an entire unicellular organism
Is the basis of sperm and egg formation
Allows for development from a single fertilized egg to an adult organism
Functions in an organism's renewal and repair

4. 8.3 Prokaryotes reproduce by binary fission
Prokaryotic cells reproduce asexually by a type of cell division called binary fission
Genes are on one circular DNA molecule
The cell replicates its single chromosome
The chromosome copies move apart
The cell elongates
The plasma membrane grows inward, dividing the parent into two daughter cells

5. LE 8-3a Prokaryotic Plasma chromosome membrane Cell wall
Duplication of chromosome
and separation of copies
Continued elongation of the
cell and movement of copies
Division into
two daughter cells

6. Prokaryotic chromosomes
LE 8-3b
Prokaryotic chromosomes 
Colorized TEM 32,500

7. THE EUKARYOTIC CELL CYCLE AND MITOSIS
8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division
Eukaryotic genes
Many more than in prokaryotes
Grouped into multiple chromosomes in the nucleus

8. Eukaryotic chromosomes
Contain a very long DNA molecule associated with proteins
Most of the time occur in the form of thin, loosely packed chromatin fibers
Condense into visible chromosomes just before cell division

10. Eukaryotic cell division Chromosomes replicate
Sister chromatids joined together at the centromere
Sister chromatids separate
Now called chromosomes
Cell divides into two daughter cells
Each with a complete and identical set of chromosomes

11. LE 8-4b
Sister chromatids
Centromere
TEM 36,600

12. LE 8-4c Chromosome duplication Sister chromatids Centromere Chromosome
distribution to
daughter
cells

13. 8.5 The cell cycle multiplies cells
The cell cycle is an ordered series of events extending from the time a cell is formed until it divides into two
Most of the cell cycle is in interphase
G1: cell grows in size
S: DNA synthesis (replication) occurs
G2: Cell continues to grow and prepare for division

14. The cell actually divides in mitotic (M) phase
Mitosis: nuclear division
Cytokinesis: cytoplasmic division
Duplicated chromosomes evenly distributed into two daughter nuclei

15. S (DNA synthesis) Cytokinesis Mitosis INTERPHASE G1 G2 MITOTIC LE 8-5
PHASE (M)

16. 8.6 Cell division is a continuum of dynamic changes
Interphase: Duplication of the genetic material ends when chromosomes begin to become visible
Prophase (the first stage of mitosis): The mitotic spindle is forming. Centrosomes migrate to opposite ends of the cell
Prometaphase: Chromatins completely coil into chromosomes; nucleoli and nuclear membrane disperse

17. Metaphase: The spindle is fully formed; chromosomes are aligned single file with centromeres on the metaphase plate
Anaphase: Chromosomes separate from the centromere, dividing to arrive at poles
Telophase: Cell elongation continues, a nuclear envelope forms around chromosomes, chromosomes uncoil, and nucleoli reappear
Cytokinesis: The cytoplasm divides

18. LE 8-6a LM 250  INTERPHASE PROPHASE PROMETAPHASE Early mitotic
spindle
Fragments
of nuclear
envelope
Centrosomes
(with centriole pairs)
Centrosome
Chromatin
Kinetochore
Nucleolus
Nuclear
envelope
Plasma
membrane
Chromosome, consisting
of two sister chromatids
Centromere
Spindle
microtubules

19. LE 8-6b Metaphase plate Cleavage furrow Nucleolus forming Nuclear
ANAPHASE
TELOPHASE AND CYTOKINESIS
Metaphase
plate
Cleavage
furrow
Nucleolus
forming
Nuclear
envelope
forming
Daughter
chromosomes
Spindle

20. Animation: Cytokinesis
8.7 Cytokinesis differs for plant and animal cells
Animals
Ring of microfilaments contracts into cleavage furrow
Cleavage occurs
Plants
Vesicles fuse into a membranous cell plate
Cell plate develops into a new wall between two daughter cells
Animation: Cytokinesis

21. LE 8-7a Cleavage furrow Cleavage furrow Cleavage furrow
SEM 140
Cleavage furrow
Contracting ring of
microfilaments
Daughter cells

22. LE 8-7b TEM 7,500 Cell plate forming Wall of parent cell Daughter
nucleus
TEM 7,500
Cell wall
New cell wall
Vesicles containing
cell wall material
Cell plate
Daughter cells

23. 8.8 Anchorage, cell density, and chemical growth factors affect cell division
An organism must be able to control the timing of cell division
Anchorage dependence
Most animal cells must be in contact with a solid surface to divide

24. Density-dependent inhibition
Cells form a single layer
Cells stop dividing when they touch one another
Inadequate supply of growth factor causes division to stop

25. LE 8-8a Cells anchor to dish surface and divide. When cells have
formed a complete
single layer, they
stop dividing
(density-dependent
Inhibition).
If some cells are
scraped away, the
remaining cells
divide to fill the dish
with a single layer
and then stop
(density-dependent
inhibition).

26. After forming a single layer, cells have stopped dividing.
LE 8-8b
After forming a
single layer,
cells have
stopped dividing.
Providing an
additional supply of
growth factors
stimulates
further cell division.

27. 8.9 Growth factors signal the cell cycle control system
The cell cycle control system regulates the events of the cell cycle
If a growth factor is not released at three major checkpoints, the cell cycle will stop
G1 of interphase
G2 of interphase
M phase

28. G0 S G1 G2 M LE 8-9a G1 checkpoint Control system M checkpoint

29. How a growth factor might affect the cell cycle control system
Cell has receptor protein in plasma membrane
Binding of growth factor to receptor triggers a signal transduction pathway
Molecules induce changes in other molecules
Signal finally overrides brakes on the cell cycle control system

30. Growth factor Plasma membrane Relay proteins Receptor protein
LE 8-9b
Growth factor
Plasma membrane
Relay
proteins
Receptor
protein
G1 checkpoint
Signal
transduction
pathway
Control
system G1 S M G2

31. 8.10 Growing out of control, cancer cells produce malignant tumors
CONNECTION
8.10 Growing out of control, cancer cells produce malignant tumors
Cancer cells do not respond normally to the cell cycle control system
Divide excessively
Can invade other tissues
May kill the organism

32. If an abnormal cell avoids destruction by the immune system, it may form a tumor
Benign: abnormal cells remain at original site
Malignant: abnormal cells can spread to other tissues and parts of the body
Metastasis: spread of cancer cells through the circulatory system

33. LE 8-10 Lymph vessels Tumor Blood vessel Glandular tissue
A tumor grows from a
single cancer cell.
Cancer cells invade
Neighboring tissue.
Cancer cells spread through
lymph and blood vessels to
other parts of the body.

34. Cancers are named according to location of origin
Carcinoma: external or internal body coverings
Sarcoma: tissues that support the body
Leukemia and lymphoma: blood-forming tissues
Radiation and chemotherapy are effective as cancer treatments because they interfere with cell division

35. 8.11 Review of the functions of mitosis: growth, cell replacement, and asexual reproduction
When the cell cycle operates normally, mitotic cell division functions in
Growth
Replacement of damaged or lost cells
Asexual reproduction
Video: Hydra Budding

39. MEIOSIS AND CROSSING OVER
8.12 Chromosomes are matched in homologous pairs
The somatic (body) cells of each species contain a specific number of chromosomes
Humans and most other organisms have pairs of homologous chromosomes
Carry genes for the same characteristics at the same place, or locus
Except sex chromosomes
One chromosome is inherited from the female parent, one from the male

40. LE 8-12
Chromosomes
Centromere
Sister chromatids

41. 8.13 Gametes have a single set of chromosomes
Diploid cells have two sets of chromosomes (2n)
Somatic cells
Haploid cells have one set of chromosomes (n)
Gametes (egg and sperm cells)
Sexual life cycles involve the alternation of haploid and diploid stages
Fusion of haploid gametes in fertilization forms a diploid zygote

42. LE 8-13 (2n = 46) Haploid gametes (n = 23) n Egg cell n Sperm cell
Meiosis
Fertilization
Diploid
zygote
(2n = 46) 2n
Multicellular
diploid adults
(2n = 46)
Mitosis and
development

43. 8.14 Meiosis reduces the chromosome number from diploid to haploid
Like mitosis, is preceded by chromosome duplication
Unlike mitosis, cell divides twice to form four haploid daughter cells

44. The process of meiosis includes two consecutive divisions Meiosis I
In synapsis, homologous chromosomes are paired
In crossing over, homologous chromosomes exchange corresponding segments
Each homologous pair divides into two daughter cells, each with one set of chromosomes consisting of two chromatids

45. Meiosis II
Essentially the same as mitosis
Sister chromatids of each chromosome separate
Result is four cells, each with half as many chromosomes as the parent

46. LE 8-14a Microtubules attached to kinetochore Centrosomes
MEIOSIS I
: Homologous chromosome separate
INTERPHASE
PROPHASE I
METAPHASE I
ANAPHASE I
Microtubules
attached to
kinetochore
Centrosomes
(with centriole
pairs)
Metaphase
plate
Sister chromatids
remain attached
Sites of crossing over
Spindle
Nuclear
envelope
Sister
chromatids
Tetrad
Centromere
(with kinetochore)
Homologous
chromosomes separate
Chromatin

47. LE 8-14b Haploid daughter Sister chromatids cells forming separate
MEIOSIS I
: Sister chromatids separate
TELOPHASE I
TELOPHASE I
PROPHASE I
METAPHASE I
ANAPHASE I
AND CYTOKINESIS
AND CYTOKINESIS
Cleavage
furrow
Sister chromatids
separate
Haploid daughter
cells forming

48. 8.15 Review: A comparison of mitosis and meiosis
Provides for growth, tissue repair, and asexual reproduction
Produces daughter cells genetically identical to the parent
Meiosis
Needed for sexual reproduction
Produces daughter cells with one member of each homologous chromosome pair

49. (before chromosome replication)
LE 8-15
MITOSIS
MEIOSIS
Parent cell
(before chromosome replication)
Site of
crossing over
MEIOSIS I
Prophase I
Prophase
Duplicated
chromosome (two
sister chromatids)
Chromosome
replication
Chromosome
replication
Tetrad formed
by synapsis of
homologous
chromosomes
2n = 4
Chromosomes
align at the
metaphase plate
Tetrads
align at the
metaphase plate
Metaphase
Metaphase I
Anaphase
Telophase
Sister chromatids
separate during
anaphase
Anaphase I
Telophase I
Homologous
chromosomes
separate during
anaphase I;
sister
chromatids
remain together
Haploid
n = 2
Daughter
cells of
meiosis I
No further
chromosomal
replication;
sister
chromatids
separate during
anaphase II 2n 2n
MEIOSIS I
Daughter cells
of mitosis n n n n
Daughter cells of meiosis II

50. Animation: Genetic Variation
8.16 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring
Reshuffling of the different versions of genes during sexual reproduction produces genetic variation
Random arrangements of chromosome pairs at metaphase I of meiosis lead to many different combinations of chromosomes
Random fertilization of eggs by sperm greatly increases this variation
Animation: Genetic Variation

51. LE 8-16 Possibility 1 Possibility 2 Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Gametes
Combination 1
Combination 2
Combination 3
Combination 4

52. 8.17 Homologous chromosomes carry different versions of genes
Each chromosome of a homologous pair can bear different versions of genes at corresponding loci
Makes gametes (and thus offspring) different from one another
Examples: coat color and eye color in mice

53. duplicated chromosomes)
LE 8-17a
Coat-color
genes
Eye-color
genes C E
Brown
Black C E C E
Meiosis c e c e c e
White
Pink
Tetrad in parent cell
(homologous pair of
duplicated chromosomes)
Chromosomes of
the four gametes

54. Brown coat (C); black eyes (E) White coat (c); pink eyes (e)
LE 8-17b
Brown coat (C); black eyes (E)
White coat (c); pink eyes (e)

55. Animation: Crossing Over
8.18 Crossing over further increases genetic variability
Crossing over is a genetic rearrangement between two homologous chromosomes
Homologues pair up into a tetrad during prophase I of meiosis
Maternal and paternal chromatids break at the same place
The two broken chromatids join together in a new way at the chiasma
Animation: Crossing Over

56. LE 8-18a
TEM 2,200
Tetrad
Chiasma
Centromere

57. When homologous chromosomes separate at anaphase I, each contains a new segment
In meiosis II, each sister chromatid goes to a different gamete
Gametes of four genetic types result

58. LE 8-18b Coat-color genes Eye-color genes C E (homologous pair of c e
Tetrad
(homologous pair of
chromosomes in synapsis) c e
Breakage of homologous chromatids C E c e
Joining of homologous chromatids C E
Chiasma c e
Separation of homologous
chromosomes at anaphase I C E C e c E c e
Separation of chromatids at
anaphase II and
completion of meiosis C E
Parental type of chromosome C e
Recombinant chromosome c E
Recombinant chromosome c e
Parental type of chromosome
Gametes of four genetic types

59. ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE
8.19 A karyotype is a photographic inventory of an individual's chromosomes
A blood sample is treated with a chemical that stimulates mitosis
After several days, another chemical arrests mitosis at anaphase, when chromosomes are most highly condensed
Chromosomes are photographed and electronically arranged by size and shape into the karyotype
Normal humans have 22 pairs of autosomes and two sex chromosomes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

60. LE 8-19 Hypotonic Fixative Packed red and solution white blood cells
Stain
Centrifuge
Blood
culture
Fluid
Centromere
Sister
chromatids
Pair of homologous
chromosomes
2,600

61. 8.20 An extra copy of chromosome 21 causes Down syndrome
CONNECTION
8.20 An extra copy of chromosome 21 causes Down syndrome
A person may have an abnormal number of chromosomes
Down syndrome is caused by trisomy 21, an extra copy of chromosome 21
The most common human chromosome number abnormality
Many physical and mental problems
Increased incidence in older mothers

64. Infants with Down syndrome
LE 8-20c 90 80 70 60
Infants with Down syndrome
(per 1,000 births) 50 40 30 20 10 20 25 30 35 40 45 50
Age of mother

65. 8.21 Accidents during meiosis can alter chromosome number
Abnormal chromosome count is a result of nondisjunction
The failure of homologous pairs to separate during meiosis I
The failure of sister chromatids to separate during meiosis II

66. Nondisjunction in meiosis I Normal meiosis II Normal meiosis II
LE 8-21a
Nondisjunction
in meiosis I
Normal
meiosis II
Normal
meiosis II
Gametes
n + 1
n + 1
n  1
n  1
Number of chromosomes

67. Normal meiosis I Nondisjunction in meiosis I Gametes n + 1 n  1 n n
LE 8-21b
Normal
meiosis I
Nondisjunction
in meiosis I
Gametes
n + 1
n  1 n n
Number of chromosomes

68. Fertilization of an egg resulting from nondisjunction with a normal sperm results in a zygote with an abnormal chromosome number
May be involved in trisomy 21

69. LE 8-21c
Egg
cell
n + 1
Sperm
cell
Zygote
2n + 1
n (normal)

70. CONNECTION
8.22 Abnormal numbers of sex chromosomes do not usually affect survival
Nondisjunction can produce gametes with extra or missing sex chromosomes
Upset the genetic balance less than unusual numbers of autosomes
Lead to varying degrees of malfunction in humans
Usually do not affect survival

72. 8.23 Alterations of chromosome structure can cause birth defects and cancer
Breakage can lead to rearrangements affecting genes on one chromosome
Deletion: loss of a fragment of chromosome
Duplication: addition of a fragment to sister chromatid
Inversion: reattachment of a fragment in reverse order
Inversions least harmful because all genes are present in normal number

73. Homologous chromosomes
LE 8-23a
Deletion
Duplication
Homologous
chromosomes
Inversion

74. Translocation is the attachment of a chromosomal fragment to a nonhomologous chromosome
Can be reciprocal
May or may not be harmful

75. LE 8-23b

76. Chromosomal changes in sperm or egg cells can cause congenital disorders
Chromosomal changes in a somatic cell may contribute to the development of cancer

77. “Philadelphia chromosome”
LE 8-23c
Chromosome 9
Reciprocal
translocation
Chromosome 22
“Philadelphia chromosome”
Activated cancer-causing gene