3. Cell division
• The process of cells undergoes division to produce new cells is called
cell division.
• Cell division of an eukaryotic cell can be divided into two stages:
nuclear division and cytoplasmic division (cytokinesis).
• Eukaryotic cells have three types of cell division:
• Amitosis无丝分裂
• Mitosis有丝分裂
• Meiosis减数分裂
4. Learning objectives
1. To understand the process and characteristics of mitosis.
2. To understand the process and characteristics of meiosis.
3. To understand the importance of cell division.
4. To understand the differences between mitosis and meiosis.
8. Cell cycle
• The cell cycle is the series of events
that take place in a cell leading to its
division and duplication of its DNA
(DNA replication) to produce two
daughter cells.
• Cell cycle includes two stages:
• Interphase (gap phase)分裂间期
• mitotic cell division (or M phase)分裂期
9. G0 phase
• Cells that does not undergo cell
division enter the G0 phase.
• Cells that are fully differentiated
such as neurons, and some kidney,
liver cells generally enter G0 phase
when mature.
• Many cells e.g., epithelial cells do
not enter G0 and continue to
divide throughout an organism‘s
life。
10. Interphase (gap phase)
• Interphase is the interval in
between the two mitotic
division.
• The cell increases in size and
replicates DNA to prepare for
cell division.
• Interphase is divided into:
• G1 (gap or growth phase 1)
• S (DNA synthesis)
• G2 (gap or growth phase 2)
11. G1 phase
• G1 phase is the time taken from the
end of mitosis until the beginning of
DNA replication.
• The cell syntheses proteins and new
cytoplasmic organelles such as
mitochondria and chloroplasts.
• The metabolic rate of the cell is high.
• The chromosomes are not condensed
and appears as chromatin.
12. S phase
• S phase is the time for the replication of
DNA.
• The cell also duplicates a microtubule-
organizing structure, the centrosome.
13. G2 phase
• G2 phase is the time taken from the end
of DNA replication until the beginning
of mitosis.
• The cell continues to grow makes
proteins and organelles.
• The begins to reorganize its contents in
preparation for mitosis.
14. Changes in the quantity of DNA
• The quantity of DNA per cell
changes according the its
phases in the cell cycles.
15. Using flow cytometry to determine the phase
• The G1/G0 phase is where the 2N amount
of DNA because there are two copies of
each chromosome in the nucleus of the
cell.
• The cells synthesis DNA during the S-
phase
• Once the cell has finished synthesizing its
DNA, it enter the G2 phase and has twice
as much as the original cell (4N).
• The cells are not all going through the
cell cycle synchronized in one phase of
the cell cycle.
16. Quiz
• Write down the phase of the
cells that correspond to each
peaks in this flow cytometry
graph.
17. Summary
• Interphase is the interval in
between the two mitotic
division.
• The cell spends much of the
time in interphase.
• After interphase, the cells now
have replicated DNA and
centrosomes.
• The cell enters M phase.
20. Mitosis
• from Greek mitos ‘thread’
• Mitosis, a process of cell
duplication, or reproduction,
during which one cell gives
rise to two genetically
identical daughter cells.
• Mitosis increases the number
of body cells.
21. M phase
• During the mitotic (M) phase, the
cell divides its copied DNA and
cytoplasm to make two new cells.
• M phase involves two distinct
division-related processes:
• Mitosis有丝分裂
• cytokinesis细胞质分裂
• The process is slightly different
between animals and plants.
22. Phases in mitosis
• Prophase
• Prometaphase
• Metaphase
• Anaphase
• Telophase + cytokinesis
Here we are going to look
at mitosis in animal.
[Please] Pee on the MAT.
23.
24. Prophase前期
• pro- ‘before’
• The chromatin in the nucleus
condenses into chromosomes
and become visible under the
light microscope.
• In the cytoplasm, the spindle
fibres纺锤体 [microtubules微小管]
begin to form between the
centrioles.
• The nucleolus disappears.
25. Structure of the chromosome in prophase
姐妹染色单体
同源染色体
着色体
S phase
Number of chromosomes 2 2
Number of sister
chromatids
0 2
Number of DNA 2N 4N
26. Prometaphase前中期
• pro- ‘before’ + meta ‘occurring or
situated behind or after’
• Nuclear envelope disintegrate.
• Chromosome moves towards the
metaphase plate赤道面.
• The mitotic spindle grows more,
and some of the microtubules start
to “capture” chromosomes at the
kinetochore着丝点.
27. Structure of mitotic spindle纺锤体
星体微管
Spindle pole 纺锤体极
微管组织中心
(i.e. centrosome中心体
in animals)
着丝点
(On centromere着色体)
极微管
动粒微管
28. Metaphase中期
• All the chromosomes align at
the metaphase plate赤道面 .
• Two kinetochores of each
chromosome attaches to
microtubules from opposite
spindle poles.
29. Anaphase后期
• Greek ana- ‘back’
• The sister chromatids
separate and are pulled
towards opposite ends of
the cell.
• Microtubules not
attached to chromosomes
elongate and push apart,
separating the poles and
making the cell longer.
30. Telephase末期
• The mitotic spindle
disaapears.
• Two nuclear membranes
and nucleoli reappear.
• The chromosomes begin to
decondense into chromatin.
31. Telophase – cytokinesis细胞质分裂
• Cytokinesis is the division of
the cytoplasm to form two
new cells.
• In animal cells, actin pinch
crease the cell inwards,
forming the cleavage furrow
分裂沟 at the metaphase
plate.
• Plant cells forms new cell
wall from the cell plate细胞板,
which are Golgi-derived
vesicles.
32.
33.
34. Quiz: Identify the mitosis stages
Write down your name, number, class and date
1
2
3
4
5
6
7
8
9
35. Comparison of interphase in plant and animal
cells
Animal cells Plant cells
G1 Increase in protein, organelles, and cellular size
S Replicate DNA and centrosome Replicate DNA
G2 Forms spidle and aster
projections
Forms spindle fibre
36. Comparison of mitosis in plant and animal cells
Animal cells Plant cells
Prophase
Chromosomes and spindle forms
Nuclear envelope disintegrate
Nucleolus disaapear
Aster forms No aster
Two centrosome separates No centrosome
Metaphase
Chromosomes line up at the metaphase plate.
Kinetochores attached with mitotic fibre
Telophase Sister chromatids moves towards opposite poles
Anaphase
Nuclear division
Chromatins reform
Spindle fibre disappear
Cytokinesis
Nuclear envelope and nucleolus reappear
Pinch forms the cleavage furrow Cell plate forms new cell wall
39. Objectives
• To understand the process and characteristics of amitosis.
• To understand the process and characteristics of meiosis.
• To distinguish between meiosis and mitosis.
• To understand the importance of meiosis and mitosis.
41. Amitosis无丝分裂
• -a ‘without’ + mitos ‘thread’
• Amitosis is cell division by simple cleavage
of the nucleus and division of the
cytoplasm without spindle formation or
appearance of chromosomes.
• The nuclear membrane and nucleolus
remain intact.
• Occurs in some prokaryotic organisms, and
plant and animal cells that are fast
growing, such as the epithelial cells of the
renal tubules, the adrenal cortical cells, and
liver cells.
42. Process of amitosis
1. Chromatin is duplicated, the size of the
nucleus and nucleolus increases. The
nucleolus organizer region separates into
two.
2. The nucleus is enlarged and ultimately forms
a dumbbell-shaped structure with the
appearance of a median constriction.
3. On the median part of the cell membrane
two constrictions are appearing.
4. The constriction of the nucleus gradually
grow deeper and divides the nucleus into two
daughter nuclei without the formation of any
spindle fibre.
5. The invaginations of the cell also move
inwards and the parent cell is divided into
two equal size of daughter cells.
44. Meiosis
• from Greek meioun ‘lessen’
• A type of cell division that
results in four daughter cells
each with half the number of
chromosomes of the parent
cell (2N N)
• Produce of gametes (e.g.
sperm and ovule) and plant
spores.
• Required longer time to
complete compare to mitosis.
45. Aim of meiosis
• Meiosis not only separate sister
chromatids (the two halves of a
duplicated chromosome), as in mitosis,
but it also separate homologous
chromosomes (the similar but
nonidentical chromosome pairs an
organism receives from its two parents).
• Meiosis I separates the homologue pairs
of chromosome.
• Meiosis II separates the sister chromatids.
• Four daughter cells in produce in the end.
46. Prophase I
• The spindle fibres begin to form between the centrioles.
• The nucleolus disappears and nuclear envelope disintegrate.
• The chromatin condenses into chromosomes.
• Each chromosome aligns with its homologue in the process of
synapse联会.
• The homologous chromosomes touch each other to exchange
genetic material in a process called crossing over染色體互換.
• The X-shape point where the chromosomes in contact is called a
chiasma 交叉 (pl. chiasmata).
• from Greek chiasma ‘crosspiece, cross-shaped mark’
• After crossing over, the spindle begins to capture chromosomes and move
them towards the metaphase plate.
• Each chromosome attaches to microtubules from just one pole of the
spindle, and the two homologues of a pair bind to microtubules from
opposite poles.
48. Metaphase I
• Homologue pairs—not individual chromosomes—
line up at the metaphase plate for separation.
• The orientation of each pair is random.
49. Anaphase I
• The homologues are pulled apart and move apart
to opposite ends of the cell.
• The sister chromatids of each chromosome remain
attached to one another.
• Microtubules not attached to chromosomes
elongate and push apart, separating the poles and
making the cell longer.
50. Telophase I
• The chromosomes arrive at opposite poles of the cell.
• The mitotic spindle disaapears.
• Cytokinesis usually occurs at the same time as telophase
I, forming two haploid daughter cells.
• In some organisms, the nuclear membrane re-forms and
the chromosomes decondense, although in others, this
step is skipped.
• The cells are haploid (N).
53. Prophase II
• Cells move from meiosis I to meiosis II without
copying their DNA.
• The chromosomes condense and the nuclear
envelope breaks down, if needed.
• The centrosomes move apart, the spindle forms
between them, and the spindle microtubules begin
to capture chromosomes.
• The two sister chromatids of each chromosome are
captured by microtubules from both the opposite
spindle poles.
54. Metaphase II
• The chromosomes line up individually along the
metaphase plate.
55. Anaphase II
• The sister chromatids separate and are pulled
towards opposite poles of the cell.
56. Telophase II
• The nuclear membranes form around each set of
chromosomes, and the chromosomes
decondense.
• Cytokinesis splits the chromosome sets into new
cells, forming four haploid cells in which each
chromosome has just one chromatid.
• In humans, the products of meiosis are sperm or
egg cells.
59. Quiz
• Which stage of meiosis II is the cell in?
1. Prophase I
2. Telophase II
3. Metaphase II
4. Anaphase II
5. Mataphase I
60. Quiz: Correctly match the following phases of
meiosis I with their events.
Prophase I Metaphase I Anaphase I Telophase I
Homologue pairs line
up in the center of the
cell.
Chromosomes arrive at
opposite poles of the
cell and the nuclear
membrane reforms.
Homologue pairs pull
apart and move to
opposite ends of the
cell.
Crossing over occurs.
X
X
X
X
61. Quiz
• When does crossing over occur during meiosis?
1. Prophase I
2. Prophase II
3. Anaphase I
4. Metaphase I
5. Telophase I
62. Quiz
• This cell is undergoing meiosis II.
• Which stage of meiosis II is the cell in?
• Prophase II
• Metaphase II
• Telophase II
• Anaphase II
Cell with single chromatids, some of them
recombinant, separating to opposite poles
63. Objectives
• To distinguish between meiosis and mitosis.
• To understand the importance of meiosis and mitosis.
65. Importance of mitosis
• Number of cells increases in order to
replace the dead or worn out cells.
• To enable the daughter cell
possesses the same number of
chromosomes as mother cell.
• One of the methods of asexual
reproduction such as binary fission二
体分裂, budding芽体生殖, nutritive
propagation / vegetative
reproduction营养繁殖etc.
69. Importance of meiosis
• Formation of haploid chromosome
gamete.
• To make sure fertilized egg cell or
zygote consists of diploid number of
chromosomes after fertilization of
the gametes.
• To increase the genetic variation of
the organisms to drive evolution.
70. How meiosis increase genetic diversity
• Crossing over during prophase I.
• The points where homologues cross over
and exchange genetic material are chosen
more or less at random, and they will be
different in each cell that goes through
meiosis.
• Random orientation of homologue
pairs during metaphase I.
• The random orientation of homologue
pairs in metaphase I allows for the
production of gametes with many different
assortments of homologous
chromosomes.
71. How can siblings look alike but not exactly the
same if they come from the same parents?
72. Importance of crossing over
• The gene combinations that
a person gets from his or her
parents will be different, to
varying degrees, than the
combination a sibling may
get.
• Crossing over increases
genetic diversity
73. Haplodiploidy 单倍二倍性
is a sex-determination
system in which males
develop from
unfertilized eggs and
are haploid, and
females develop from
fertilized eggs and are
diploid.
孤雌生殖
75. Differences between mitosis and meiosis
Mitosis Meiosis
Number of division 1 2
Number of daughter
cells
2 4
Site of the process
Generally, happens in the cells
such as skin, cambium etc.
Occurs in the reproductive
organs such as testes, ovary,
anther, ovule etc.
Prophase
Simpler
i. No synapsis happened
ii. No tetrad produced
iii.No crossing over
More complicated
i. Synapsis happened
ii. Tetrad produced
iii.Crossing over happened
Number of
chromosomes
Remains unchanged
Half of the chromosomes of
parent cell
https://www.youtube.com/watch?v=l1qvUPYDnOY
The first 42 seconds is microscopy of a developing egg cell from a mouse which is very similar to a human early embryo. The subsequent stages are filmed on larger scale silicone models with movement in the later stages being created through puppetry. the film was originally shot for the National Geographic series of "In the Womb".
