2. CELL DIVISION
• It’s the process by which a cell divides to
form two new cells
• • Three types of cell division or cell
reproduction in an organism
• • Prokaryotes (bacteria)
- Binary fission
- • Divides forming two new identical cells
3. • Eukaryotes
-Mitosis
• Cell or organism growth • Replacement or
repair of damaged cells
-Meiosis • formation of sex cells, or gametes
4. WHY DO CELLS DIVIDE?
• Cells divide for growth, development,
repair of worn-out tissues and
reproduction
• To facilitate the exchange of materials
• To control DNA overloading
5. PROKARYOTIC CELL
DIVISION
• 1. Binary Fission
• Three (3) major steps;
• DNA Replication DNA is copied resulting into two
identical chromosomes
• Chromosome Segregation Chromosomes
separate and move towards ends (poles) of cell
• Cytokinesis (Separation) Cytoplasm divides
forming two (2) cells
• Each new daughter cell is Genetically Identical to
parent cell
6.
7. EUKARYOTIC CELL DIVISION
• Cell division that results in two daughter cells each
having the same number and kind of chromosomes
as the parent cell
• 1. MITOSIS
• Two (2) main steps:
1. Mitosis
• Fours steps;
[Prophase>Metaphase>Anaphase>Telophase]
2. Cytokinesis
• Cytoplasm divides forming two new daughter cells
• Each daughter cell is Genetically Identical to parent
cell
8.
9. • Cell division that results in four daughter cells
2. MEIOSIS
• Two (2) major steps:
1. Mitosis Fours steps;
[Prophase>Metaphase>Anaphase>Telophase]
2. Cytokinesis
• Cytoplasm divides forming two new daughter
cells
• Each daughter cell is NOT Genetically Identical to
parent cell
10. THE CELL CYCLE
• The sequence of events from the time a cell first
arises as a result of cell division until the time when
that cell itself divides.
• Arise – Divide
• This consist of periods of;
• Growth and Development
• DNA Replication
• Preparation For Division
• Cell Division
• Cell after division begins a new cycle
11. The Cell Cycle
• Consist of two(2) main periods;
I. Interphase
II. Mitotic Phase
12. Interphase
• Interphase: period of growth and DNA replication
between cell divisions
• Three (3) phases:
• G1 Phase ‒ Cell increases in size
• S Phase ‒ Replication of DNA ‒ Two sister strands
of DNA called chromatids are produced
• G2 Phase ‒ Organelles double ‒ New cytoplasm
forms ‒ All other structures needed for mitosis form
14. Mitotic Phase
• Mitotic phase is the stage when a cell divides
• Mitosis – the division of a single nucleus into two
genetically identical daughter nuclei • This division
involves two(2) processes;
‒ Division of the nucleus
‒ Separation of the cytoplasm and the new nuclei
into daughter cells
15. Mitotic Phase
• Divided into two (2) mitotic phases
• 1st Mitotic Phase contain four stages (P-
MAT)
‒ Prophase, metaphase, anaphase and
telophase
• 2nd Mitotic Phase is cytokinesis
17. Interphase
• The period when the cell is in a non-dividing state
• A cell spends most of its time in this phase
• During this time it grows, replicates its
chromosomes and prepares for cell division.
• The cell then leaves interphase, undergoes
mitosis, and completes its division.
18. Early Prophase
• Chromatids condense becoming chromosomes
• Nucleolus disappears
• Centrioles separate and start moving to opposite
ends of the cell
• Spindle begins to form
19. Late Prophase
• The nuclear membrane fragments and the
microtubules invade the nuclear area
• Centrioles have moved to the opposite poles
• The spindle is completely formed
20. Metaphase
• The chromosomes are aligned at the metaphase
plate
• Centrioles move at polar ends and projects
spindle fibers to connect each chromosome
21. Anaphase
• The paired chromosomes (sister chromatids)
separate
• Separated chromatids move to opposite pole
• Partial division of cytoplasm begins
22. Telophase
• Chromosomes are at the poles
• Chromosomes uncoil-turn chromatin
• Nuclear envelops reforms
• Spindle fiber disappear
23. Cytokinesis
• Occurs at the end of mitosis
• Animal cells: a cleavage furrow separates the
daughter cells
• Plant cell: a cell plate separates the daughter cells
• Daughter cells are genetically identical
24. CONTROL OF THE CELL
CYCLE
• Regulatory proteins called cyclins control the cell
cycle at checkpoints:
• G1 Checkpoint—decides whether or not cell will
divide
• S Checkpoint—determines if DNA has been
properly replicated
• Mitotic Spindle Checkpoint—ensures
chromosomes are aligned at mitotic plate
25. Eukaryotic Cell Cycle
– Cell grows.
– DNA is replicated.
– Mitotic cell division produces
daughter cells identical to the
parent.
– Repeat.
The timing of replication and
cell division is highly
regulated.
Image: Cell cycle by Richard Wheeler From the Virtual Cell Biology Classroom on ScienceProfOnline.com
26. Image: Cell cycle by Richard Wheeler From the Virtual Cell Biology Classroom on ScienceProfOnline.com
2 major phases:
• Interphase (3 stages)
– DNA is not condensed
• Mitosis (4 stages + cytokinesis)
– Nuclear division & division of
cytoplasm
– DNA condensed
Eukaryotic Cell Cycle
27. Interphase
Non-dividing state
with 3 sub-stages:
Gap 1 – cell grows in size
– organelles replicated
Synthesis – replication of DNA
– synthesis of proteins
associated with DNA
Gap 2 – synthesis of proteins
associated with mitosis
Image: Cell cycle by Richard Wheeler; Interphase in Onion Cell
Drawing & Photo, Source Unknown From the Virtual Cell Biology Classroom on ScienceProfOnline.com
28. Mitosis
Division of somatic cells (non-reproductive
cells) in eukaryotic organisms.
A single cell divides into two identical
daughter cells.
Daughter cells have same number of
chromosomes as does parent cell.
29. Packing for the move…
When the cell is not dividing…
• DNA molecules are in extended,
uncondensed form = chromatin
• Cell can only replicate and
transcribe DNA when it is in the
extended state.
When the cell is preparing for
division…
• DNA molecules condense to form
chromosomes prior to division.
• each chromosome is a single
molecule of DNA
• easier to sort and organize the
replicated DNA into daughter cells
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
30. Mitosis
4 sub-phases:
1st – Prophase
2nd – Metaphase
3rd – Anaphase
4th – Telophase
followed by
Cytokinesis
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Image: Mitosis diagram, Marek Kultys
31. 1. Prophase
Three Major Events
1. chromosomes
condense
2. spindle fibers form
1. (spindle fibers are
specialized microtubules
radiating out from centrioles)
3. chromosomes are captured by spindle
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
chromatin
nucleolus
nucleus
centrioles
condensing
chromosomes
32. • chromosomes align along the
equator of the cell, with one
chromatid facing each pole
centrioles
spindle fibers
chromosomes
2. Metaphase
Images: Metaphase drawing, Henry Gray's Anatomy of the Human Body;
Metaphase Onion Cell Drawing & Photo, Source Unknown
33. 3. Anaphase
• sister chromatids separate
• spindle fibers attached to
kinetochores shorten and pull
chromatids towards the poles.
• free spindle fibers lengthen and
push the poles of the cell apart
Images: Anaphase drawing, Henry Gray's Anatomy of the Human Body;
Anaphase Onion Cell Drawing & Photo, Source Unknown From the Virtual Cell Biology Classroom on ScienceProfOnline.com
34. 4. Telophase
• spindle fibers disintegrate
• nuclear envelopes form around both groups
of chromosomes
• chromosomes revert to their extended state
• cytokinesis occurs, enclosing each daughter
nucleus into a separate cell
Images: Telophase drawing, Henry Gray's Anatomy of the Human Body;
Telophase Onion Cell Drawing & Photo, Source Unknown From the Virtual Cell Biology Classroom on ScienceProfOnline.com
35. Cytokinesis – Plant vs. Animal Cell
• Plant cells undergo cytokinesis
by forming a cell plate between
the two daughter nuclei.
• Animal cells undergo
cytokinesis through the
formation of a cleavage furrow. A
ring of microtubules contract,
pinching the cell in half.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Images: Telophase drawing, Henry Gray's Anatomy of the Human Body; Ciliate
dividing, TheAlphaWolf; Telophase Onion Cell Photo, Source Unknown
36. - A single germ cell divides into four unique daughter cells.
- Daughter cells have half the # of chromosomes as parent cell, so
they are considered haploid.
Image: Overview of Meiosis,
National Institutes of Health
What is cell division of gametes called?
Meiosis
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
37. Diploid organisms receive one of each type of
chromosome from female parent (maternal chromosomes) and
one of each type of chromosome from male parent
(paternal chromosomes)
Refers to the number of sets of
chromosomes in cells.
● Haploid – one copy of each chromosome
– designated as “n”, the number of
chromosomes in one “set”
– gametes
● Diploid – two sets of chromosomes (two of
each chromosome)
– designated as “2n”
– somatic cells
Genetics Terminology: Ploidy
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
38. Genetics Terminology: Homologues
Chromosomes exist in homologous pairs in
diploid (2n) cells.
Exception: Sex chromosomes (X, Y).
All other chromosomes (autosomes) have homologues.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
39. Karyotype
• Q: How many homologous
pairs are in each
karyotype?
• Q: How is the bottom
karyotype different from
the top two?
Image: Karyotype, National Human Genome Research Institute
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
40. Sexual Reproduction
• Fusion of two gametes to
produce a single zygote.
• Introduces greater genetic
variation, allows genetic
recombination.
• Zygote has gametes from
two different parents
(except in cases of self-
fertilizing organisms).
Rose + Greg = Steven
Images: Rose, Greg, and Steven, Steven Universe From the Virtual Cell Biology Classroom on ScienceProfOnline.com
41. Sexual reproduction in humans …
• At fertilization, 23 chromosomes
are donated by each parent.
(total = 46 or 23 pairs).
• Gametes (sperm/ova):
– Contain 22 autosomes and 1 sex
chromosome.
– Are haploid (haploid number “n” = 23
in humans).
• Fertilization results in diploid zygote.
– Diploid cell; 2n = 46. (n = 23 in humans)
• Q: Most cells in the body are produced through what type of cell division?
(Remember, only gametes are produced through meiosis)
Image: Superficial human anatomy, Mikael
Häggström& Rainer Zenz; Sperm & egg, Wikipedia From the Virtual Cell Biology Classroom on ScienceProfOnline.com
42. Meiosis - Sex Cell (Gamete) Formation
In meiosis, there
are 2 divisions
of the nucleus:
meiosis I
&
meiosis II
Image: Overview of Meiosis,
National Institutes of Health From the Virtual Cell Biology Classroom on ScienceProfOnline.com
43. Image: Meiosis diagram, Marek Kultys
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
44. Meiosis & Sexual Reproduction
Life Cycle
Image: Animal Life Cycle, Dr. T’s Bio 328 Genetics
Mitosis * *
*
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
45. Genetic Variation in Diploid Organisms
Fusion of sperm and egg results in unique
offspring…
…but not only because the young are a product
of two individuals with different genetic
makeup.
Meiosis also “shuffles” the genes so that the
an individual’s gametes are genetically
different from one another.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com Image: Meiosis diagram, Marek Kultys
How is this shuffling accomplished?
46. Genetic shuffling of Meiosis I
In addition to a new combination of chromosomes resulting from
fertilization, there are also events in Meiosis I that shuffle the
genes.
1. Crossing over in Prophase I.
2. Independent assortment in Metaphase I.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
47. Crossing Over
• Homologues break at identical
locations, then rejoin opposite
partners.
• This creates new combinations
of the alleles on each
chromosome.
• Occurs randomly several times
on every chromosome.
• Results in mixing of the genes
you inherited from your
parents.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
49. Variation from genetic
recombination
• Independent assortment of chromosomes
– meiosis introduces genetic variation
– gametes of offspring do not have same
combination of genes as gametes from parents
• random assortment in humans produces
223 (8,388,608) different combinations in gametes
from Dad
from Mom offspring
new gametes
made by offspring
50. Mitosis vs. Meiosis
• 2n
• Clone
• Same genetic
information in parent
cell and daughter cell.
• Give me another one
just like the other
one!
• 1n
• Daughter cells different
from parent cell and from
each other.
• Daughter cells have ½ the
number of chromosomes
as somatic cell.
• Shuffling the genes
(Mix it up!)
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
51. Image: Mitosis diagram & Meiosis diagram, Marek Kultys From the Virtual Cell Biology Classroom on ScienceProfOnline.com
52. Drawing and Labeling Chromosomes
Sister
Chromatid
Replicated
Uncondensed
Chromosome
(chromatin)
Sister
Chromatid
Centromere
Unreplicated
Uncondensed
Chromosome
(chromatin)
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
53. Drawing & Labeling Homologous Chromosomes
Unreplicated,
Condensed,
Homologous
Chromosomes
Replicated,
Condensed,
Homologous
Chromosomes
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
