Cellular
Division
1
Purpose of Cell Division:
In prokaryotes: Asexual
reproduction
In eukaryotes: Make new cells
for growth and replace damaged
or old cells
2
Keeping Cells Identical
The instructions for
cells are in the
DNA.
Each new cell must
get a complete set
of the DNA.
3
DNA Replication
DNA must be
Original DNA
copied or
strand
replicated
before cell
division
Two new,
identical DNA
Each daughter
strands
cell will receive
an identical copy
of the DNA
4
Identical Daughter Cells
Two
identical
daughter
cells
Parent Cell
5
Chromosomes
6
Prokaryotic Chromosome
In prokaryotes
(bacteria), DNA
is one, circular
chromosome
Prokaryotes also
have plasmids –
small, extra
pieces of DNA.
7
Cell Division in
Prokaryotes
8
Cell Division in Prokaryotes
 Prokaryotes divide
Parent
into 2 identical cells
cell
by the process of
binary fission
 First, the single
Chromosome
chromosome makes a relicates
copy of itself
 The cell splits
Cell splits
 A cell wall forms
between the new cells
2 identical daughter cells
9
Prokaryotic Cell
Undergoing Binary Fission
10
Eukaryotic Cells have
chromosomes
Most eukaryotes have between 10
and 50 chromosomes in their body
cells
Human body cells have 46
chromosomes or 23 identical pairs
11
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
12
Compacting DNA into
Chromosomes
During
division,
DNA is
tightly
coiled
around
histone
proteins
13
Chromosomes in Dividing Cells
Before division,
chromosomes
replicate.
Duplicated
chromosomes are
called
chromatids &
are held
together by the
centromere
Called Sister Chromatids
14
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
15
Boy or Girl?
The Y Chromosome Decides
Y - Chromosome
X - Chromosome
16
Cell Reproduction in
Eukaryotes
17
The events in eukaryotic
cell division are described
as the Cell Cycle
18
Phases of the Cell Cycle
Phase 1 – Interphase
3 parts:
G1 - primary growth phase
S – synthesis; DNA replicated
G2 - secondary growth phase
Phase 2 – mitosis
Phase 3 - cytokinesis
19
Interphase - G1 Stage
Cells grow and mature by making
more cytoplasm & organelles
20
Interphase – S Stage
Synthesis stage
DNA is copied or replicated
Two
identical
copies
of DNA
Original
DNA
21
Interphase – G2 Stage
2nd Growth Stage
All the cell structures that are
needed for division are made (e.g.
centrioles)
22
Mitosis
23
Mitosis
Doesn’t occur in
some cells such
as brain cells
Has four stages
24
Four Mitotic Stages
Prophase
Metaphase
Anaphase
Telophase
25
Early Prophase
Chromatin in nucleus condenses (gets
thick) to form visible chromosomes
Mitotic spindle forms
Nucleolus
Cytoplasm
Nuclear Membrane
Chromosomes
26
Late Prophase
Nuclear membrane & nucleolus are
broken down
Spindle fibers attach to the
centromere of each chromosome
27
Late Prophase
Chromosomes
Nucleus & Nucleolus have disintegrated
28
Metaphase
Chromosomes move to the center of
the cell and line up at the equator
Equator of Cell
Pole of
the Cell
29
Metaphase
Asters at
the poles
Spindle
Fibers
Chromosomes
lined at the
Equator
30
Metaphase
Aster
Chromosomes at Equator
31
Anaphase
Sister
chromatids are
pulled apart to
opposite poles
of the cell
32
Anaphase
Sister
Chromatids
being
separated
33
Telophase
Sister chromatids reach opposite
poles
Nuclear envelope forms around
each set of sister chromatids
Nucleolus reappears
CYTOKINESIS occurs
34
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
35
Cytokinesis
Cleavage furrow
in animal cell
Cell plate in
plant cell
36
Mitotic Stages
37
Daughter Cells of Mitosis
Have the same number of
chromosomes as the parent cell
Identical to each other, but smaller
than parent cell
Must grow in size to become mature
cells (G1 of Interphase)
38
Review
of
Mitosis
39
Review:
Interphase
Name this?
Prophase
Telophase
Name this?
Metaphase
Anaphase
40
Eukaryotic Cell Division
 Cells are diploid (2n)
Prophase
Metaphase
Anaphase Telophase Cytokinesis
41
Mitosis Animation
Name each stage as you see it occur?
42
Mitosis in Onion Root Tips
Do you see any stages of mitosis?
43
Draw & Learn these Stages
44
Draw & Learn these Stages
45
Test Yourself
over Mitosis
46
Mitosis Quiz
47
Mitosis Quiz
48
Name the Stages of Mitosis:
Early Anaphase
Early prophase
Metaphase
Interphase
Late
Prophase
Late telophase,
Mid-Prophase
Advanced
cytokinesis
Early
Telophase,
Begin
cytokinesis
Late
Anaphase
49
Identify the Stages
?
Early, Middle, & Late Prophase
?
?
Metaphase
Late Prophase
Late Anaphase
Anaphase
?
?
Telophase
?
?
Telophase &
Cytokinesis
50
Locate the Four Mitotic
Stages in Plants
Anaphase
Telophase
Metaphase
Prophase
51
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
52
Meiosis
Formation of Gametes
(Eggs & Sperm)
53
Facts About Meiosis
Two meiotic divisions --- Meiosis
I and Meiosis II
Called Reduction- division
Original cell is diploid (2n)
Four daughter cells produced that
are monoploid (1n)
54
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)
55
More Meiosis Facts
 Start
with 46 double stranded
chromosomes (2n)
After division - 23 chromosomes
(1n)

56
Why Do we Need Meiosis?
Two haploid (1n) gametes are
brought together through
fertilization to form a diploid
(2n) zygote
57
Fertilization – “Putting it
all together”
2n = 6
1n =3
58
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
59
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!
60
Meiosis: Two Part Cell
Division
Sister
chromatids
separate
Homologs
separate
Meiosis
I
Meiosis
II
Diploid
Diploid
Haploid
61
Prophase I
Early prophase
Homologs pair.
Crossing over
occurs.
62
Homologs form Tetrads
Homologous chromosomes
(each with sister
chromatids)
Join to form a
TETRAD
Called Synapsis
63
Crossing-Over
 Homologous
chromosomes in
a tetrad cross
over each other
 Pieces of
chromosomes or
genes are
exchanged
 Produces
Genetic
recombination in
the offspring
64
Crossing-Over
Crossing-over multiplies the already huge
number of different gamete types
65
Results of Meiosis
Gametes (egg & sperm)
form
Four haploid cells with
one copy of each
chromosome
66
Gametogenesis
Oogenesis
or
Spermatogenesis
67
Spermatogenesis
Meiosis in the
testes
Two divisions
produce 4
spermatids
Spermatids mature
into sperm
Men produce about
250,000,000
sperm per day
68
Spermatogenesis in the
Testes
Spermatid
69
Oogenesis
Meiosis 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
70
Oogenesis in the Ovaries
71
Comparing
Mitosis and
Meiosis
72
Comparison of Divisions
Mitosis
Meiosis
2
Number of
divisions
1
Number of
daughter cells
2
4
Yes
No
Same as parent
Half of parent
Where
Somatic cells
Germ cells
When
Throughout life
At sexual maturity
Growth and
repair
Sexual reproduction
Genetically
identical?
Chromosome #
Role
73
74