Cellular
Reproduction
1
Types of Cell Reproduction
Asexual reproduction involves a
single cell dividing to make 2 new,
identical daughter cells
3 Reasons why cells undergo asexual
Reproduction:
1. Growth
2. Repair
3. Replacement
 Examples: somatic cells (body), cancer cells
2
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
M - mitosis
C - cytokinesis
3
The Cell Cycle
DNA Copied
Cells
Mature
Daughter
Cells
Cells prepare for
Division
Cell Divides into
Identical cells
http://www.cellsalive.com/mitosis.htm
4
Interphase
• Occurs before Mitosis begins
• Chromosomes are copied (# doubles)
• Chromosomes appear as threadlike coils
(chromatin) at the start, but each chromosome
and its copy (sister chromosome) change to
sister chromatids at end of this phase
 Remember:
 G1 - primary growth phase
 S – synthesis; DNA replicated
 G2 - secondary growth phase
**collectively these 3 stages are called
interphase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
5
Mitosis
Division of the
nucleus
Also called
karyokinesis
Only occurs in
eukaryotes (plants
and animal cells)
Has four stages
Doesn’t occur in
some cells such as
brain cells
6
Four Mitotic Stages
Prophase
Metaphase
Anaphase
Telophase
7
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
8
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
9
Late Prophase
Chromosomes
Nucleus & Nucleolus have disintegrated
10
Review of Prophase
What the cell
looks like
What’s happening
11
Metaphase
Chromosomes, attached to the kinetochore
fibers, move to the center of the cell
Chromosomes are now lined up at the
equator
Metaphase= “Middle”
Equator of Cell
Pole of
the Cell
12
Metaphase
The poles
of a cell
Spindle
Fibers
Chromosomes
lined at the
Equator
13
Metaphase
The pole of
the cell
Animal Cell
Plant Cell
Chromosomes at
Equator
14
Review of Metaphase
What the cell looks
like
What’s
occurring
15
Anaphase
Occurs
rapidly
Sister
chromatids
are pulled
apart to
opposite poles
of the cell by
spindle fibers
Sister
Chromatids
being
separated
16
Anaphase Review
What the
cell looks
like
What’s
occurring
17
Telophase
Sister chromatids at opposite poles
Spindle disassembles
Two new nuclei form
Nuclear envelope forms around each
set of sister chromatids
Nucleolus reappears
CYTOKINESIS occurs
Chromosomes reappear as chromatin
18
Comparison of Anaphase & Telophase
19
Telophase
Animal Cell
Plant Cell
Nuclei reforming
Polar microtubules
continue elongation
20
Cytokinesis
Means division of the cytoplasm
Occurs after mitosis
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
21
Cytokinesis
Cleavage furrow
in animal cell
Cell plate in
plant cell
22
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)
23
Review Eukaryotic Cell Division
 Used for growth and
repair
 Produce two new cells
identical to the original
cell
 Cells are diploid (2n)
Prophase
Metaphase
Chromosomes during
Metaphase of mitosis
Anaphase Telophase Cytokinesis
24
Mitotic Stages
25
The Cell Cycle Animation
You should be able to name each stage!!
26
Review
of
Mitosis
27
Name the Mitotic Stages:
Interphase
Name this?
Prophase
Telophase
Name this?
Metaphase
Anaphase
28
Mitosis in Onion Root Tips
Do you see any stages of mitosis?
29
Draw & Learn these Stages
30
Draw & Learn these Stages
31
Test Yourself
over Mitosis
32
Mitosis Quiz
33
Mitosis Quiz
34
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
35
Identify the Stages
?
Early, Middle, & Late Prophase
?
?
Metaphase
Late Prophase
Late Anaphase
Anaphase
?
?
Telophase
?
?
Telophase &
Cytokinesis
36
Locate the Four Mitotic
Stages in Plants
Anaphase
Telophase
Metaphase
Prophase
37
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
38
Meiosis
Formation of Gametes
(Eggs & Sperm)
39
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)
40
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)
41
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 that
produce gametes
42
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
43
Fertilization – “Putting it
all together”
2n = 6
1n =3
44
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
45
A Replicated Chromosome
Gene X
Homologs
(same genes,
different alleles)
Sister
Chromatids
(same genes,
same alleles)
Homologs separate in meiosis I and
therefore different alleles separate.
46
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!
47
Meiosis: Two Part Cell
Division
Sister
chromatids
separate
Homologs
separate
Meiosis
I
Meiosis
II
Diploid
Diploid
Haploid
48
Meiosis I: Reduction Division
Spindle
fibers
Nucleus
Early
Prophase I
(Chromosome
number
doubled)
Late
Prophase
I
Nuclear
envelope
Metaphase
Anaphase Telophase I
I
I
(diploid)
49
Prophase I
Early prophase
Homologs pair.
Crossing over
occurs.
Late prophase
Chromosomes condense.
Spindle forms.
Nuclear envelope
fragments.
50
Tetrads Form in Prophase I
Homologous chromosomes
(each with sister
chromatids)
Join to form a
TETRAD
Called Synapsis
51
Crossing-Over
 Homologous
chromosomes in
a tetrad cross
over each other
 Pieces of
chromosomes or
genes are
exchanged
 Produces
Genetic
recombination in
the offspring
52
Homologous Chromosomes
During Crossing-Over
53
Crossing-Over
Crossing-over multiplies the already huge
number of different gamete types
produced by independent assortment 54
Metaphase I
Homologous pairs
of chromosomes
align along the
equator of the
cell
55
Anaphase I
Homologs separate and
move to opposite poles.
Sister chromatids remain
attached at their
centromeres.
56
Telophase I
Nuclear envelopes
reassemble.
Spindle disappears.
Cytokinesis divides cell
into two.
57
Meiosis II
Gene X
Only one homolog of each
chromosome is present in
the cell.
Sister chromatids carry
identical genetic
information.
Meiosis II produces gametes with
one copy of each chromosome and
thus one copy of each gene.
58
Meiosis II: Reducing
Chromosome Number
Prophase
II
Metaphase
Telophase
II
Anaphase
4 Identical
II
II
haploid cells
59
Prophase II
Nuclear envelope
fragments.
Spindle forms.
60
Metaphase II
Chromosomes align
along equator of cell.
61
Anaphase II
Equator
Pole
Sister chromatids
separate and
move to opposite
poles.
62
Telophase II
Nuclear envelope
assembles.
Chromosomes
decondense.
Spindle disappears.
Cytokinesis divides
cell into two.
63
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
64
Gametogenesis
Oogenesis
or
Spermatogenesis
65
Spermatogenesis
Occurs in the
testes
Two divisions
produce 4
spermatids
Spermatids mature
into sperm
Men produce about
250,000,000
sperm per day
66
Spermatogenesis in the
Testes
Spermatid
67
Spermatogenesis
68
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
69
Oogenesis in the Ovaries
70
Oogenesis
First polar body
may divide
(haploid)
a
Mitosis
Oogonium
(diploid)
X
A
X
Primary
oocyte
(diploid)
X
a
X
a
a
Polar
bodies
die
X
Meiosis I Meiosis II
(if fertilization
A
occurs)
X
A
X
Secondary
oocyte
(haploid)
Ovum (egg) Mature
egg
A
X
Second
polar body
(haploid)
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