The document covers the principles of cell division, including the cell cycle phases, mitosis, cytokinesis, and meiosis. It explains the structure of chromosomes, the processes involved in cell division, and the importance of the cell cycle control system in ensuring proper division. Additionally, it describes the difference between asexual and sexual reproduction, the functions of various cellular components, and the implications of uncontrolled mitosis, such as cancer.

1. Chapter 1
PRINCIPLES OF ANIMAL LIFE – II
ZOL-302
Cell Division
By
Nawabzada Ch Dr Yasir Sardar
03009196932
yasir.haadi@gmail.com
1

2. Learning Objectives
• The cell cycle and its phases.
• The cell division(mitosis)
• Cytokinesis
• Cell cycle control system
• The different abnormalities of cell
cycle (cancer).
• The basis of sexual reproduction;
gamete formation.
Nawabzada Ch Dr M Yasir

3. Key Words
• Chromosome
• chromatin
• centriole & centrosome
• centromere & kinetochore
• chromatid
Nawabzada Ch Dr M Yasir

4. Chromosome
A chromosome is a
long, continuous
piece of DNA which
contains the genetic
information for a cell.
Nawabzada Ch Dr M Yasir

5. Chromatin
Chromatin is the building
block for a chromosome. It
consists of DNA and proteins.
Nawabzada Ch Dr M Yasir

6. centromere & kinetochore
• The centromere is constricted region of
the chromosomes that holds the sister
chromatids together, the site where
kinetochore forms.
• The kinetochore is a complex protein
containing structure to which
microtubules attach.
Nawabzada Ch Dr M Yasir

7. 7
Prokaryotic Chromosome
The DNA of
prokaryotes
(bacteria) is one,
circular
chromosome
attached to the
inside of the cell
membrane

8. 8
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. 9
Eukaryotic Chromosomes
Each chromosome is composed of a
single, tightly coiled DNA molecule
Chromosomes can’t be seen when
cells aren’t dividing and are called
chromatin

10. 10
Compacting DNA into
Chromosomes
DNA is
tightly
coiled
around
proteins
called
histones
Nawabzada Ch Dr M Yasir

11. 11
Chromosomes in Dividing Cells
Duplicated
chromosomes are
called
chromatids &
are held
together by the
centromere
Called Sister Chromatids

12. 12
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. 13
Boy or Girl?
Y - Chromosome
X - Chromosome
The Y Chromosome Decides

14. Centriole & centrosome
A centriole is a barrel microtubule structure.
Two centrioles arrange themselves
perpendicularly to form a centrosome.

15. 15
Cell Division
All cells are derived from pre-
existing cells
New cells are produced for
growth and to replace damaged or
old cells
Differs in prokaryotes (bacteria)
and eukaryotes (protists, fungi,
plants, & animals)
Nawabzada Ch Dr M Yasir

16. 16
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

17. 17
DNA Replication
DNA must be
copied or
replicated
before cell
division
Each new cell
will then have an
identical copy of
the DNA
Original DNA
strand
Two new,
identical DNA
strands

18. 18
Identical Daughter Cells
Parent Cell
Two
identical
daughter
cells

19. 19
Cell Reproduction
Nawabzada Ch Dr M Yasir

20. 20
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

21. 21
Cell Division in
Prokaryotes

22. 22
Cell Division in Prokaryotes
 Prokaryotes such as
bacteria divide into 2
identical cells by the
process of binary
fission
 Single chromosome
makes a copy of
itself
 Cell wall forms
between the
chromosomes dividing
the cell
Parent
cell
2 identical daughter cells
Chromosome
doubles
Cell splits

23. 23
Prokaryotic Cell
Undergoing Binary Fission

24. 24
Animation of Binary Fission
Nawabzada Ch Dr M Yasir

25. 25
The Cell
Cycle
Nawabzada Ch Dr M Yasir

26. The cell cycle is the sequence of
growth and division of a cell. It consists
of three major phases:
o interphase
o mitosis
o cytokinesis
• Cell division results in two cells that
are both identical to the parent cell.
Define cell cycle:

27. 27
Five Phases of the Cell Cycle
G1 - primary growth phase
S – synthesis; DNA replicated
G2 - secondary growth phase
collectively these 3 stages are
called interphase (Estimated
90% of cycle)
M - mitosis
C - cytokinesis

28. 28
Cell Cycle

29. 29
Interphase - G1 Stage
1st growth stage after cell
division
Cells mature by making more
cytoplasm & organelles
Cell carries on its normal
metabolic activities

30. • Growth of cell.
• Dupliction of
organelles.
• Synthisis of proteins.
G1 phase
Nawabzada Ch Dr M Yasir

31. 31
Interphase – S Stage
Synthesis stage
DNA is copied or replicated
Two
identical
copies
of DNA
Original
DNA

32. 32
Interphase – G2 Stage
2nd Growth Stage
Occurs after DNA has been copied
All cell structures needed for
division are made (e.g. centrioles)
Both organelles & proteins are
synthesized

33. • Cell continues to grow and if a problem
occurs in DNA replication, it will be
repaired.
• Cell will prepare for mitosis.
• cell synthesizes proteins needed for cell
division
G2 phase

34. 34
What’s Happening in Interphase?
What the cell looks like
Animal Cell
What’s occurring
Nawabzada Ch Dr M Yasir

35. 35
Sketch the Cell Cycle
Daughter
Cells
DNA Copied
Cells
Mature
Cells prepare for
Division
Cell Divides into
Identical cells

36. 36
Mitosis
Nawabzada Ch Dr M Yasir

37. 37
Mitosis
Division of the
nucleus
Also called
karyokinesis
Only occurs in
eukaryotes
Has four stages
Doesn’t occur in
some cells such
as brain cells

38. Mitosis
• is the process in which a eukaryotic
cell separates the chromosomes in
its cell nucleus, into two identical
sets in two daughter cells.

39. Estimated (10% of
cycle)
Includes 2 parts :
1)Mitosis
•Prophase
•Promataphase
•Metaphase
•Anaphase
•Telophase
M phase

40. 40
Four Mitotic Stages
Prophase
Metaphase
Anaphase
Telophase

41. Prophase
•
Duration (15 min)
Chromosomes condense
(get thicker) and coil,
they become visible under
light microscope.
• The two sister chromatids of
each chromosomes attach at a
point called centromere.
• Spindle fibers begin to form
from two centrosome, and they
will start moving apart.

42. 42
Early Prophase
Chromatin in nucleus condenses to
form visible chromosomes
Mitotic spindle forms from fibers in
cytoskeleton or centrioles (animal)
Chromosomes
Nucleolus Cytoplasm
Nuclear Membrane

43. 43
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

44. 44
Late Prophase
Nucleus & Nucleolus have disintegrated
Chromosomes

45. 45
Spindle Fiber attached to
Chromosome
Kinetochore Fiber
Chromosome

46. 46
Review of Prophase
What the cell
looks like
What’s happening
Nawabzada Ch Dr M Yasir

47. 47
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

48. 48
Sketch The Spindle

49. •
Duration (15 min)
The nuclear
membrane
disappears.
• Kinetochores will get
attached to the
centromere.
• The spindle fibers
become attached to the
kinetochore.
Prometaphase

50. •
Duration (20 min)
Chromosomes reach their
most highly condensed
state.
• The spindle fibers begin to
contract to the centromeres
of the chromosomes, which
are now arranged along the
middle of the spindle.
Metaphase

51. 51
Metaphase
Chromosomes, attached to the
kinetochore fibers, move to the center
of the cell
Chromosomes are now lined up at the
equator
Pole of
the Cell
Equator of Cell

52. 52
Metaphase
Chromosomes
lined at the
Equator
Asters at
the poles
Spindle
Fibers

53. 53
Metaphase
Aster
Chromosomes at Equator

54. 54
Review of Metaphase
What the cell looks
like
What’s
occurring
Nawabzada Ch Dr M Yasir

55. •
Duration (3 min)
The centromere of each
chromosome splits, allowing
the sister chromatids to
separate.
• The chromatids are then pulled
by the spindle fibers toward
opposite sides of the cell.
• The two sets of chromosomes
are identical.
•
Cleavage furrow starts to
form.
Anaphase:

56. 56
Anaphase
Occurs rapidly
Sister
chromatids are
pulled apart to
opposite poles
of the cell by
kinetochore
fibers

57. 57
Anaphase
Sister
Chromatids
being
separated

58. 58
Anaphase Review
What the
cell looks
like
What’s
occurring

59. •
Duration (10 min)
New nuclear membranes are
formed around each of the two
sets of 46 chromosomes.
• The spindle fibers
disappear.
• Chromosomes become
thinner.
•
•
Cytoplasm starts dividing by
contractile ring.
At the end, we will have two diploid
daughter cells, which are identical.
Telophase:

60. 60
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

61. 61
Comparison of Anaphase & Telophase

62. 62
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
Nawabzada Ch Dr M Yasir

63. Cytokinesis
•
•
the division of the cytoplasm
and organelles
Begin in anaphase and
completed by the end of
telophase .

64. 64
Cytokinesis
Cleavage furrow
in animal cell
Cell plate in
animal cell

65. 65
Mitotic Stages
Nawabzada Ch Dr M Yasir

66. 66
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)

67. 67
Identical Daughter Cells
Chromosome number the same, but cells
smaller than parent cell
What is
the 2n
or
diploid
number?
2

68. 68
Review
of
Mitosis
Nawabzada Ch Dr M Yasir

69. 69
Draw & Learn these Stages

70. 70
Draw & Learn these Stages

71. 71
Interphase
Prophase
Metaphase
Anaphase
Telophase
Name the Mitotic Stages:
Name this?
Name this?
Nawabzada Ch Dr M Yasir

72. 72
Eukaryotic Cell Division
 Used for growth and
repair
 Produce two new cells
identical to the original
cell
 Cells are diploid (2n)
Chromosomes during
Metaphase of mitosis
Prophase Metaphase Anaphase
Telophase
Cytokinesis
Nawabzada Ch Dr M Yasir

73. 73
Mitosis Animation
Name each stage as you see it occur?
Nawabzada Ch Dr M Yasir

74. Summary
• Interphase (90% of cycle)
o G1 phase~ growth
o S phase~ synthesis of
DNA
o G2 phase~ preparation for
cell division
• Mitotic phase (10% of
cycle)
o Mitosis~ nuclear division
o Cytokinesis~
cytoplasm division

75. Cell cycle control
system
Nawabzada Ch Dr M Yasir

76. Cell cycle control system
Involves
•Cell cycle checkpoints
•Specialized protein complex
Function control the order and timing of
the cell cycle.

77. ( control points )
They are pathways that:
•Ensure that events are completed correctly
before letting the cell enter the next phase.
The checkpoint receive signals from : inside
and outside the cell
Checkpoints

78. There are 3 major checkpoints :
I.at the end of G1
it is large & strong enough to continue with the cell division
process
II.at the end of G2
III.during mitosis phase
it ensures if the spindles attached to the kinetochore within
each chromosome
Checkpoints

80. Is a combination of a Cycline & Cdk*
to preform its work ( help the cell to enter the next
phase) it has to be activated by phosphorylated at one
site and dephosphorylated at the other site.
* Cycline dependent
kinase
Specialized
protein complex

81. Cell Cycle
M
I
T
O
S
I
S
interphase
prophase
metaphase
anaphase
telophase
cytokinesis
Chromosomes invisible; DNA replicates
Chromosomes appear, nucleus
disappears
Chromatids pulled to poles
Cytoplasmic division
Chromosomes at equator, spindle forms
Chromatids at poles, nucleus reforms

82. Cell Increase and Decrease
•
•
•
Cell division:
oMitosis
oCytokinesis
Apoptosis (cell death) decreases the
number of cells.
Both cell increase and apoptosis occur
during normal development and growth.

83. 83
Test Yourself
over Mitosis
Nawabzada Ch Dr M Yasir

84. 84
Mitosis Quiz

85. 85
Mitosis Quiz

86. 86
Name the Stages of Mitosis:
Interphase
Early prophase
Mid-Prophase
Late
Prophase
Metaphase
Late
Anaphase
Early Anaphase
Early
Telophase,
Begin
cytokinesis
Late telophase,
Advanced
cytokinesis

87. 87
Identify the Stages
Early, Middle, & Late Prophase
Late Prophase
Metaphase Anaphase
Late Anaphase Telophase Telophase &
Cytokinesis
?
? ? ?
? ? ?

88. Now we’ll see how much
you’ve learned
so raise your hand and wait
your turn...
Nawabzada Ch Dr M Yasir

89. 89
Locate the Four Mitotic
Stages
Metaphase
Prophase
Anaphase
Telophase
Nawabzada Ch Dr M Yasir

90. 90
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

91. 91
Meiosis
Formation of Gametes
(Eggs & Sperm)
Nawabzada Ch Dr M Yasir

92. 92
Facts About Meiosis
Preceded by interphase which
includes chromosome replication
Two meiotic divisions --- Meiosis
I and Meiosis II
Called Reduction- division
Original cell is diploid (2n)
Four daughter cells produced that
are monoploid (1n)

93. 93
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)

94. 94
 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 that
produce gametes
More Meiosis Facts

95. 95
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

96. 96
Fertilization – “Putting it
all together”
1n =3
2n = 6
Nawabzada Ch Dr M Yasir

97. 97
Replication of Chromosomes
Replication is the
process of
duplicating a
chromosome
Occurs prior to
division
Replicated copies
are called sister
chromatids
Held together at
centromere
Occurs in
Interphase

98. 98
A Replicated Chromosome
Homologs
(same genes,
different alleles)
Sister
Chromatids
(same genes,
same alleles)
Gene X
Homologs separate in meiosis I and
therefore different alleles separate.

99. 99
Meiosis Forms Haploid Gametes
 Meiosis must reduce the chromosome number
by half
 Fertilization then restores the 2n number
from mom from dad child
meiosis reduces
genetic content
too
much!
The right
number!

100. 100
Meiosis: Two Part Cell
Division
Homologs
separate
Sister
chromatids
separate
Diploid
Meiosis
I
Meiosis
II
Diploid
Haploid

101. 101
Meiosis I: Reduction Division
Nucleus Spindle
fibers Nuclear
envelope
Early
Prophase I
(Chromosome
number
doubled)
Late
Prophase
I
Metaphase
I Anaphase
I
Telophase I
(diploid)

102. 102
Prophase I
Early prophase
Homologs pair.
Crossing over
occurs.
Late prophase
Chromosomes condense.
Spindle forms.
Nuclear envelope
fragments.

103. 103
Tetrads Form in Prophase I
Homologous chromosomes
(each with sister
chromatids)
Join to form a
TETRAD
Called Synapsis

104. 104
Crossing-Over
 Homologous
chromosomes in
a tetrad cross
over each other
 Pieces of
chromosomes or
genes are
exchanged
 Produces
Genetic
recombination in
the offspring

105. 105
Homologous Chromosomes
During Crossing-Over

106. 106
Crossing-over multiplies the already huge
number of different gamete types
produced by independent assortment
Crossing-Over

107. 107
Metaphase I
Homologous pairs
of chromosomes
align along the
equator of the
cell

108. 108
Anaphase I
Homologs separate and
move to opposite poles.
Sister chromatids remain
attached at their
centromeres.

109. 109
Telophase I
Nuclear envelopes
reassemble.
Spindle disappears.
Cytokinesis divides cell
into two.

110. 110
Meiosis II
Only one homolog of each
chromosome is present in
the cell.
Meiosis II produces gametes with
one copy of each chromosome and
thus one copy of each gene.
Sister chromatids carry
identical genetic
information.
Gene X

111. 111
Meiosis II: Reducing
Chromosome Number
Prophase
II
Metaphase
II
Anaphase
II
Telophase
II 4 Identical
haploid cells

112. 112
Prophase II
Nuclear envelope
fragments.
Spindle forms.
Nawabzada Ch Dr M Yasir

113. 113
Metaphase II
Chromosomes align
along equator of cell.

114. 114
Anaphase II
Sister chromatids
separate and
move to opposite
poles.
Equator
Pole

115. 115
Telophase II
Nuclear envelope
assembles.
Chromosomes
decondense.
Spindle disappears.
Cytokinesis divides
cell into two.

116. 116
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

117. 117
Gametogenesis
Oogenesis
or
Spermatogenesis
Nawabzada Ch Dr M Yasir

118. 118
Spermatogenesis
Occurs in the
testes
Two divisions
produce 4
spermatids
Spermatids mature
into sperm
Men produce about
250,000,000
sperm per day

119. 119
Spermatogenesis in the
Testes
Spermatid

120. 120
Spermatogenesis

121. 121
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

122. 122
Oogenesis in the Ovaries

123. 123
Oogenesis
Oogonium
(diploid)
Mitosis
Primary
oocyte
(diploid)
Meiosis I
Secondary
oocyte
(haploid)
Meiosis II
(if fertilization
occurs)
First polar body
may divide
(haploid)
Polar
bodies
die
Ovum (egg)
Second
polar body
(haploid)
a
A
X
X
a
X
A X
a
X
a
X
Mature
egg
A
X
A
X

124. 124
Comparing
Mitosis and
Meiosis
Nawabzada Ch Dr M Yasir

125. 125
Mitosis Meiosis
Number of
divisions
1
2
Number of
daughter cells
2 4
Genetically
identical?
Yes No
Chromosome # Same as parent Half of parent
Where Somatic cells Germ cells
When Throughout life At sexual maturity
Role
Growth and
repair
Sexual reproduction
Comparison of Divisions
Nawabzada Ch Dr M Yasir

126. If you have any Question
raise your hand and wait
your turn...
Nawabzada Ch Dr M Yasir