1. Cellular
Division
Unicellular: for reproduction
Multicellular: growth/repair of damaged body parts
Renewal/repair of worn out cells
1

2. Words to know
• DNA/RNA
• Chromosomes - organized structure of DNA and
protein
• Chromatins - mass of genetic material composed
of DNA and proteins that condense to form
chromosomes during eukaryotic cell division
• Chromatids - each of the two threadlike strands
into which a chromosome divides longitudinally
during cell division. Each contains a double helix
of DNA.
2

3. Cell Division
All cells are derived from pre-
existing cells
New cells are produced for
growth and to replace damaged or
old cells
Allows the cell to pass DNA copy
to daughter cells
Differs in prokaryotes (bacteria)
and eukaryotes (protists, fungi,
plants, & animals)
3

4. Keeping Cells Identical
The instructions for
making cell parts
are encoded in the
DNA, so each new
cell must get a
complete set of the
DNA molecules
4

5. DNA Replication
DNA must be
copied or Original DNA
strand
replicated
before cell
division Two new,
identical DNA
Each new cell strands
will then have an
identical copy of
the DNA
5

6. Identical Daughter Cells
Two
identical
daughter
cells
Parent Cell
6

7. Chromosomes
structure within the cell
that bears the genetic or as a circular
material as a threadlike strand of DNA (or
linear strand of DNA RNA in some
bonded to various viruses) in the
proteins in the nucleus cytoplasm of
of eukaryotic cells prokaryotes
7

8. Prokaryotic Chromosome
The DNA of
prokaryotes
(bacteria) is one,
circular
chromosome
attached to the
inside of the cell
membrane
8

9. Eukaryotic Chromosomes
All eukaryotic cells store genetic
information in chromosomes
Most eukaryotes have between 10 and
50 chromosomes in their body cells
Human body cells have 46 chromosomes
or 23 identical pairs
9

10. Eukaryotic Chromosomes
Each chromosome is composed of a
single, tightly coiled DNA molecule
Chromosomes can’t be seen (with a
microscope) when cells aren’t
dividing and are called chromatin
10

11. Compacting DNA into
Chromosomes
DNA is
tightly
coiled
around
proteins
called
histones
11

12. Chromosomes in Dividing Cells
Duplicated
chromosomes are
called
chromatids &
are held
together by the
centromere
Called Sister Chromatids 12

13. Karyotype
A picture of the
chromosomes from a
human cell arranged
in pairs by size
First 22 pairs are
called autosomes
Last pair are the
sex chromosomes
XX female or XY
male
13

14. Boy or Girl?
The Y Chromosome Decides
Y - Chromosome
X - Chromosome
14

15. Cell Reproduction
15

16. Types of Cell Reproduction
Asexual reproduction involves a
single cell dividing to make 2 new,
identical daughter cells
Mitosis & binary fission are
examples of asexual reproduction
Sexual reproduction involves two
cells (egg & sperm) joining to make a
new cell (zygote) that is NOT
identical to the original cells
Meiosis is an example
16

17. Division Mechanisms
Prokaryotic organisms
– Binary fission
Eukaryotic organisms
– Mitosis
• Karyokinesis (division of nucleus)
• Cytokinesis (division of cytoplasm)
– Meiosis

18. Cell Division in
Prokaryotes
18

19. Cell Division in Prokaryotes
 Prokaryotes such as
Parent
bacteria divide into 2
cell
identical cells by the
process of binary
fission Chromosome
 Single chromosome doubles
makes a copy of
itself
Cell splits
 Cell wall forms
between the
chromosomes dividing
the cell
2 identical daughter cells 19

20. Prokaryotic Cell
Undergoing Binary Fission
20

21. Animation of Binary Fission
21

22. The Cell
Cycle
22

23. Five Phases of the Cell Cycle
G1 - primary growth/gap phase
S – synthesis; DNA replicated
G2 - secondary growth/gap
phase
collectively these 3 stages are
called interphase
M - mitosis
C - cytokinesis
23

24. Cell Cycle
24

25. Interphase - G1 Stage
1st growth/gap stage after cell
division
Cells mature by making more
cytoplasm & organelles
Cell carries on its normal
metabolic activities i.e.
respiration, digestion etc.
25

26. Interphase – S Stage
Synthesis stage
DNA is copied or replicated
Two
identical
copies
of DNA
Original
DNA
26

27. Interphase – G2 Stage
2nd Growth/Gap Stage
Occurs after DNA has been copie;
also in preparation for M phase
All cell structures needed for
division are made (e.g. centrioles)
Both organelles & proteins are
synthesized
27

28. What’s Happening in Interphase?
What the cell looks like
Animal Cell
What’s occurring
28

29. Sketch the Cell Cycle
DNA Copied
Cells prepare for
Cells Division
Mature
Daughter
Cells
Cell Divides into
Identical cells
29

30. Mitosis
30

31. Mitosis
Division of the
nucleus
(karyokinesis)
Division of the
cytoplasm
(cytokinesis)
Only occurs in
eukaryotes
Has four stages
Doesn’t occur in
some cells such as
brain cells
31

32. Four Mitotic Stages
Prophase
Metaphase
Anaphase
Telophase
32

33. Early Prophase
Chromatin in nucleus condenses to
form visible chromosomes
Mitotic spindle forms from fibers in
cytoskeleton or centrioles (animal)
Nucleolus Cytoplasm
Nuclear Membrane
Chromosomes
33

34. Late Prophase
Nuclear membrane & nucleolus are
broken down
Chromosomes continue condensing &
are clearly visible
Spindle fibers called kinetochores
attach to the centromere of each
chromosome
Spindle finishes forming between the
poles of the cell
34

35. Late Prophase
Chromosomes
Nucleus & Nucleolus have disintegrated
35

36. Spindle Fiber attached to
Chromosome
Kinetochore Fiber
Chromosome
36

37. Review of Prophase
What the cell
looks like
What’s happening 37

38. Spindle Fibers
The mitotic spindle form from the
microtubules in plants and centrioles
in animal cells
Polar fibers extend from one pole of
the cell to the opposite pole
Kinetochore fibers extend from the
pole to the centromere of the
chromosome to which they attach
Asters are short fibers radiating
from centrioles
38

39. Sketch The Spindle
39

40. Metaphase
Chromosomes, attached to the
kinetochore fibers, move to the center
of the cell
Chromosomes are now lined up at the
equator Equator of Cell
Pole of
the Cell
40

41. Metaphase
Asters at
the poles
Spindle Chromosomes
Fibers lined at the
Equator
41

42. Metaphase
Aster
Chromosomes at Equator
42

43. Review of Metaphase
What the cell looks
like
What’s
occurring
43

44. Anaphase
Occurs rapidly
Sister
chromatids are
pulled apart to
opposite poles
of the cell by
kinetochore
fibers
44

45. Anaphase
Sister
Chromatids
being
separated
45

46. Anaphase Review
What the
cell looks
like
What’s
occurring
46

47. Telophase
Sister chromatids at opposite
poles
Spindle disassembles
Nuclear envelope forms around
each set of sister chromatids
Nucleolus reappears
CYTOKINESIS occurs
Chromosomes reappear as
chromatin
47

48. Comparison of Anaphase & Telophase
48

49. Cytokinesis
Means division of the cytoplasm
Division of cell into two,
identical halves called daughter
cells
In plant cells, cell plate forms
at the equator to divide cell
In animal cells, cleavage furrow
forms to split cell
49

50. Cytokinesis
Cleavage furrow Cell plate in
in animal cell animal cell
50

51. Mitotic Stages
51

52. Daughter Cells of Mitosis
Have the same number of
chromosomes as each other and as
the parent cell from which they
were formed
Identical to each other, but smaller
than parent cell
Must grow in size to become mature
cells (G1 of Interphase)
52

53. Identical Daughter Cells
What is
the 2n
or
diploid
number?
2
Chromosome number the same, but cells
smaller than parent cell
53

54. Review
of
Mitosis
54

55. Draw & Learn these Stages
55

56. Draw & Learn these Stages
56

57. Name the Mitotic Stages:
Interphase
Name this?
Prophase
Telophase
Name this?
Metaphase
Anaphase
57

58. Eukaryotic Cell Division
 Used for growth and
repair
 Produce two new cells
identical to the original
cell Chromosomes during
Metaphase of mitosis
 Cells are diploid (2n)
Prophase Metaphase Anaphase Telophase Cytokinesis
58

59. Mitosis Animation
Name each stage as you see it occur?
59

60. Mitosis in Onion Root Tips
Do you see any stages of mitosis?
60

61. Test Yourself
over Mitosis
61

62. Mitosis Quiz
62

63. Mitosis Quiz
63

64. Name the Stages of Mitosis:
Early prophase
Early Anaphase Metaphase
Interphase Early
Telophase,
Begin
cytokinesis
Late Late telophase,
Prophase Advanced Mid-Prophase Late
cytokinesis Anaphase
64

65. Identify the Stages
?
Early, Middle, & Late Prophase
? ? ?
Metaphase Anaphase
Late Prophase
? ? ?
Late Anaphase Telophase Telophase &
Cytokinesis 65

66. Locate the Four Mitotic
Stages in Plants
Anaphase
Telophase
Metaphase
Prophase
66

67. Uncontrolled Mitosis
 If mitosis is not
controlled, unlimited
cell division occurs
causing cancerous
tumors
 Oncogenes are special
proteins that
increase the chance
that a normal cell
develops into a tumor
cell
Cancer cells
67

68. Meiosis
Formation of Gametes
(Eggs & Sperm)
68

69. Words to know
Gametes - reproductive cells that unite during sexual
reproduction to form a new cell called a zygote (male = sperm,
female = egg cell)
Germ cells – sperm or egg cells
Somatic cells - any cell other than the reproductive cells
Diploid - a cell that contains two sets of chromosomes (2n), as
normally found in somatic cells
Haploid - have one set of chromosomes (n=1) as in germ cells,
or half as many as a somatic cell
Homologous – chromosomes that are alike in structure and
genes
Alleles – different forms of a gene ex. if talking about hair color
as the gene, different alleles would be different colors like red,
blonde, black etc. 69

70. Facts About Meiosis
Preceded by interphase which
includes chromosome replication
Two meiotic divisions: Meiosis I
and Meiosis II
Aka reduction-division
Original cell is diploid (2n)
Four daughter cells produced that
are haploid (n)
70

71. Facts About Meiosis
Daughter cells contain half the number
of chromosomes as the original cell
Produces gametes (eggs & sperm)
Occurs in the testes in males
(Spermatogenesis)
Occurs in the ovaries in females
(Oogenesis)
Human diploid cells have 46 chromosomes
(2n=46)
Human sperm and egg cells have 23
chromosomes (n=23) each 71

72. More Meiosis Facts
 Start with 46 double stranded
chromosomes (2n)
After 1 division - 23 double
stranded chromosomes (n)
After 2nd division - 23 single
stranded chromosomes (n)
 Occurs in our germ cells
72

73. Why Do we Need Meiosis?
It is the fundamental basis of
sexual reproduction
Two haploid (1n) gametes are
brought together through
fertilization to form a diploid
(2n) zygote
73

74. Fertilization – “Putting it
all together”
2n = 6
1n =3
74

75. Replication of Chromosomes
Replication is the
process of
duplicating a Occurs in
chromosome Interphase
Occurs prior to
division
Replicated copies
are called sister
chromatids
Held together at
centromere
75

76. A Replicated Chromosome
Gene X
Homologues Sister
(same genes, Chromatids
different alleles) (same genes,
same alleles)
Homologues separate in meiosis I and
therefore different alleles separate.
76

77. Meiosis Forms Haploid Gametes
 Meiosis must reduce the chromosome number
by half
 Fertilization then restores the 2n number
from mom from dad child
too
much!
meiosis reduces
genetic content
The right
number!
77

78. Meiosis: Two Part Cell
Division
Sister
chromatids
Homologues separate
separate
Meiosis Meiosis
I II
Diploid
Diploid
Haploid
78

79. Meiosis I: Reduction Division
Nucleus Spindle
fibers Nuclear
Early envelope
Prophase I Late Metaphase
(Chromosome Prophase I Anaphase Telophase I
number I I (diploid)
doubled)
79

80. Prophase I
Early prophase Late prophase
Homologues Chromosomes condense.
pair. Spindle forms.
Crossing over Nuclear envelope
occurs. fragments.
80

81. Tetrads Form in Prophase I
Homologous chromosomes Join to form a
(each with sister chromatids) TETRAD
Called Synapsis
81

82. Crossing-Over
 Homologous
chromosomes in a
tetrad cross over
each other
 Pieces of
chromosomes or
genes are •Occurs in nonsister chromatids
exchanged •Increases genetic variability
 Produces Genetic
recombination in
the offspring
Genetic recombination in
which a strand of the genetic
material (DNA/RNA)is broken
and then joined to the end of
a different DNA molecule. 82

83. Homologous Chromosomes
During Crossing-Over
83

84. Crossing-Over
Crossing-over multiplies the already huge
number of different gamete types
produced by independent assortment
84

85. Metaphase I
Homologous pairs
of chromosomes
align along the
equator of the
cell
85

86. Anaphase I
Homologues separate and
move to opposite poles.
Sister chromatids remain
attached at their
centromeres.
86

87. Telophase I
Nuclear envelopes
reassemble.
Spindle disappears.
Cytokinesis divides cell
into two.
87

88. Meiosis II
Only one homologue of each
Gene X
chromosome is present in
the cell.
cell
Sister chromatids carry
identical genetic
information.
Meiosis II produces gametes with
one copy of each chromosome and
thus one copy of each gene.
88

89. Meiosis II: Reducing
Chromosome Number
Prophase Metaphase
II Telophase
II
Anaphase II 4 Identical
II haploid cells
89

90. Prophase II
Nuclear envelope
fragments.
Spindle forms.
90

91. Metaphase II
Chromosomes align
along equator of cell.
91

92. Anaphase II
Equator
Pole
Sister chromatids
separate and
move to opposite
poles.
92

93. Telophase II
Nuclear envelope
assembles.
Chromosomes
decondense.
Spindle disappears.
Cytokinesis divides
cell into two.
93

94. Results of Meiosis
Gametes (egg & sperm)
form
Four haploid cells with
one copy of each
chromosome
One allele of each gene
Different combinations of
alleles for different
genes along the
chromosome
94

95. Gametogenesis
Oogenesis
or
Spermatogenesis
95

96. Spermatogenesis
Occurs in the
testes
Two divisions
produce 4
spermatids
Spermatids mature
into sperm
Men produce about
250,000,000
sperm per day
96

97. Spermatogenesis in the
Testes
Spermatid
97

98. Spermatogenesis
98

99. Oogenesis
Occurs in the ovaries
Two divisions produce 3 polar bodies
that die and 1 egg
Polar bodies die because of unequal
division of cytoplasm
Immature egg called oocyte
Starting at puberty, one oocyte
matures into an ovum (egg) every 28
days
99

100. Oogenesis in the Ovaries
100

101. Oogenesis
First polar body
may divide a
(haploid) X
a Polar
bodies
a
X die
a X
X
Mitosis Meiosis I Meiosis II
A X (if fertilization
Oogonium occurs) A
(diploid) Primary
X
oocyte
(diploid) A X Ovum (egg) Mature
Secondary A egg
oocyte X
(haploid) Second
polar body
(haploid)
101

102. Comparing
Mitosis and
Meiosis
102

103. Comparison of Divisions
Mitosis Meiosis
Number of 2
1
divisions
Number of
2 4
daughter cells
Genetically
Yes No
identical?
Chromosome # Same as parent Half of parent
Where Somatic cells Reproductive cells
When Throughout life At sexual maturity
Growth and
Role Sexual reproduction
repair 103

104. Meiosis Mitosis
A type of cellular reproduction in A process of asexual reproduction
which the number of chromosomes in which the cell divides in two
Definition: are reduced by half through the producing a replica, with an equal
separation of homologous number of chromosomes in haploid
chromosomes in a diploid cell. cell
Cellular Reproduction & general
Function: sexual reproduction
growth and repair of the body
Type of Reproduction: Sexual Asexual
Occurs in: Humans, animals, plants, fungi all organisms
Genetically: different identical
Yes, mixing of chromosomes can
Crossing Over: No, crossing over cannot occur.
occur.
Pairing of Homologues: Yes No
Number of Divisions: 2 1
Number of Haploid Daughter Cells
4 2
produced:
Chromosome Number: Reduced by half Remains the same
The steps of meiosis are
The steps of mitosis are
Interphase, Prophase I, Metaphase
Interphase, Prophase, Metaphase,
Steps: I, Anaphase I, Telophase I,
Anaphase, Telophase and
Prophase II, Metaphase II,
Cytokinesis
Anaphase II and Telophase II.
Karyokenesis: Occurs in Interphase I Occurs in Interphase
Occurs in Telophase I & Telohpase
Cytokenesis: Occurs in Telophase
II
The centromeres do not separate
The centromeres split during
Centromeres Split: during anaphase I, but during
Anaphase
anaphase II
Sex cells only: Female egg cells or Makes everything other than sex
Creates: 104

105. Quiz #1
1. The stage of the cell cycle where each
chromosome is composed of 2 chromatids in
preparation for mitosis.
a. G1 c. M
b. S d. G2
2. Which of the following distinguishes prophase I
of meiosis from prophase of mitosis?
a. Homologue chromosomes pair up
b. Spindle forms
c. nuclear membrane breaks down
d. chromosomes become visible
105

106. 3. Which sequence of the cell cycle is
common to eukaryotes?
a. G1, G2, S, M, cytokinesis
b. G1, M, G2, S, cytokinesis
c. G1, S, M, G2, cytokinesis
d. G1, S, G2, M, cytokinesis
4. A cell with forty two chromosomes divides
mitotically. How many chromosomes will
each gamete have?
a. 21 c. 84
b. 42 d. 168 106

107. 5. If given the allele brown, which among the
genes below is it NOT an alternative form
of?
a. Hair color c. Nail color
b. Skin color d. Eye color
6. Meiosis results in:
a. 2 haploid daughter cells
b. 4 haploid daughter cells
c. 2 diploid daughter cells
d. 4 diploid daughter cells
107

108. 7. Which of the following cells undergo
meiosis?
a. Sperm cells c. Brain cells
b. Kidney cells d. All of the above
8. Which refers to the region of attachment
for two sister chromatids?
a. Centriole c. Microtubule
b. Cenromere d. Spindle fiber
108

109. 9. How many chromosomes are there in a
mature human cell?
a. No chromosomes
b. 26 pairs of chromosomes
c. 44 chromosomes and X and Y chromosomes
d. 50 chromosomes
10. Cytokinesis occurs during which phase of
meiosis?
a. Telophase c. Prophase
b. Anaphase d. Metaphase
109

110. 110