Cell Division & Cell Cycle
Comparing Mitosis and
Meiosis
1
Cell Division
•Cell Division-when a parent cell divides
into two daughter cells.
•All body cells are somatic cells and divide
by mitosis
•Sperm and egg, which are gametes (sex
cells) divide by meiosis
2
Cell Division
• Mitosis-the
nucleus of the cell
divides equally
Parent Cell
Two
identical
daughter
cells
3
Eukaryotic Cell Cycle
Period between cell division
DNA is Copied
Cells Synthesis phase
Mature
Gap 1 phase
Daughter
Cells
Organelles form &
Cells prepares to
Divide
Gap 2 phase
Cytoplasm Divides Cell nucleus divides equally
4
Cell Cycle
Remember: I
•
•
•
•
•
•
P M A T
C
I = Interphase (G1, S, G2)
P = Prophase
M= Metaphase
A= Anaphase
T= Telophase
C= Cytokinesis
5
Interphase: Part 1 of Cell Cycle
• Interphase-cell
prepares for cell
division.
•Has 3 phases: G1, S, G2
• Genetic Material
(DNA)-is in the form of
chromatin-uncoiled
chromosomes
6
Eukaryotic Chromosomes
• Eukaryote cells store
genetic info.in tightly
coiled DNA segments
or chromosomes
• Human body cells =46
chromosomes
Chromosomes can’t be
seen when cells aren’t
dividing and are
called chromatin
• Chromatin-uncoiled
chromosomes
7
Chromosome Pictures
• Duplicated
chromosomes are
called sister
chromatids &
are held
together by the
centromerefound at the
center of the
chromosome
Sister Chromatids
8
Mitosis: Part 2 Of Cell Cycle
• Mitosis-is equal
division of the
nucleus of
eukaryote cells
Has four stages:
• P rophase
• Metaphase
• Anaphase
• Telophase
9
Prophase
• Prophase-first and longest
phase of mitosis
• Nucleolus and nuclear
envelope will disappear
• Chromosomes are now visible
and are attached to the
spindle
• The Spindle-(a fan-like
structure that pulls the
chromosomes apart) appears.
• Centrioles-(two tiny
structures in the cytoplasm
that travel toward opposite
sides of the nucleus) in animal
cells help to form the spindle
10
Metaphase
• Second, shortest phase of mitosis; lasts a few
minutes
• Chromosomes are now lined up at the equator or
center of the cell
Equator of Cell
Pole of
the Cell
11
Anaphase
Spindle is pulling the sister
chromatids apart
Spindle
sister chromatids
Sister
Chromatids
being
separated
12
Telophase
• Sister chromatids
are at opposite poles
• Spindle breaks apart
• Nuclear envelope
forms around each
set of sister
chromatids
• Nucleolus reappears
• Chromosomes
reappear as
chromatin
13
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
14
Identical Daughter Cells
Mitosis-goes from diploid to diploid
46
46
46
What is the 2n
or diploid
chromosome
number in
humans?
46
Chromosome number is maintained or is the
same (Diploid), but cells smaller than
parent cell
15
Meiosis
Formation of Gametes
(Eggs & Sperm)
16
Facts About Meiosis
• Interphase occurs before meiosis;
chromosome replication occurs
• Two meiotic divisions-Meiosis I and
Meiosis II
• Called Reduction Division-chromosome
# is reduced by ½ (4623)
• Original cell is diploid (2n)=46
• Four daughter cells produced at the
end of meiosis are monoploid (n) or
haploid (chromosomes reduced by ½)
17
Facts About Meiosis
• Daughter cells contain half (23) the
number of chromosomes as the
original cell (46)
• Meiosis produces gametes (eggs &
sperm)
• Occurs in the testes in males
(Spermatogenesis)
• Occurs in the ovaries in females
(Oogenesis)
18
Why Do we Need Meiosis?
• It is the fundamental basis of
sexual reproduction
• Two haploid (n) gametes are
brought together through
fertilization to form a diploid
(2n) zygote
19
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!
20
Prophase I
Early prophase
•Homologs pair.
•Crossing over
occurs.
Late prophase
•Chromosomes condense.
•Spindle forms.
•Nuclear envelope
fragments.
21
Crossing-Over
• Homologous
chromosomes in
a tetrad cross
over each other
• Pieces of
chromosomes or
genes are
exchanged
• Produces
Genetic
recombination in
the offspring
22
Metaphase I
Homologous pairs
of chromosomes
align along the
equator of the
cell
23
Anaphase I
Homologs separate and
move to opposite poles.
Sister chromatids remain
attached at their
centromeres.
24
Telophase I
Nuclear envelopes
reassemble.
Spindle disappears.
Cytokinesis divides cell
into two.
25
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.
26
Meiosis II: Reducing
Chromosome Number
Prophase
II
Metaphase
Telophase
II
Anaphase
4 Identical
II
II
haploid cells
27
Prophase II
Nuclear envelope
fragments.
Spindle forms.
28
Metaphase II
Chromosomes align
along equator of cell.
29
Anaphase II
Equator
Pole
Sister chromatids
separate and
move to opposite
poles.
30
Telophase II
Nuclear envelope
assembles.
Chromosomes
decondense.
Spindle disappears.
Cytokinesis divides
cell into two.
31
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
32
Spermatogenesis
• Occurs in the
testes
• Two divisions
produce 4
spermatids
• Spermatids mature
into sperm
• Men produce about
250,000,000
sperm per day
33
Spermatogenesis in the
Testes
Spermatid
34
Oogenesis
• Occurs in the ovaries
• Two divisions produce 3 polar bodies
that die and 1 functional egg
• Polar bodies die because of unequal
division of cytoplasm
• Immature egg is called an oocyte
• Starting at puberty, one oocyte
matures into an ovum (egg) every 28
days
35
Comparing Mitosis and Meiosis
Mitosis
Meiosis
2
Number of
divisions
1
Number of
daughter cells
2
4
Yes
No
Chromosome #
Same as parent
Half of parent
Where
Somatic (body)
cells
Germ cells
When
Throughout life
At sexual maturity
Genetically
identical?
Role
Growth and
Sexual reproduction36
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
37
Nondisjunction
• When chromosomes fail to
separate during Anaphase
I or Anaphase II of
meiosis
• Chromosome number can
be more (47) or less (45),
than the normal
chromosome number (46)
• Example: Down’s
Syndrome-has extra
chromosome on #21 also
called Trisomy 21
38
Quiz
1. If a cat has 38 chromosomes in each of
its body cells, how many chromosomes will
be in each daughter cell after mitosis?
F
G
H
J
11
19
38
76
39
Quiz
2. If a cat has 38 chromosomes in each of
its cells, how many chromosomes will
be in each gamete after meiosis?
F
G
H
J
11
19
38
76
40
Quiz
3. Which of these symbols represents the
normal karyotype of a human female?
F
G
H
J
XXY
XX
XO
XXX
41
Quiz
4. This human karyotype is
unusual because
chromosome set —
Unusual Human Karyotype
A 5 has chromosomes of
different shapes
B 10 is missing genetic
material
C 14 has enlarged
centromeres
D 21 has extra genetic
material
42
Quiz
5. The diagram represents
the chromosomes of a
person with a genetic
disorder caused by
nondisjunction, in which
the chromosomes fail to
separate properly. Which
chromosome set displays
nondisjunction?
F 2
G 8
H 21
J 23
43
Quiz
6.
44
Quiz
7.
45
Quiz
8.
46
9.
47
Quiz
10.
48