Bellwork
Domestic horses have 64 chromosomes. How
many chromosomes should be in an egg cell
of a female horse?
A. 16
B. 32
C. 64
D. 128
Agenda 12/4- Cell Cycle,
Division (Mitosis)
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Bellwork
Lab: DNA extraction from strawberries
New Information: Cell Cycle, Mitosis
Homework: Identifying Stages of the Cell
Cycle- virtual lab
DNA Extraction Lab
• We’ll read through the lab procedure together.
• You can use this same procedure to extract
DNA from any living thing (including your own
DNA!)
• Safety is critical! No gum, no food, no drinks.
Always assume chemicals are dangerous! (even
though these are relatively safe if you don’t
consume them).
Bellwork 12/7
• What are the 4 phases of the cell cycle?
• What are the 4 phases of mitosis?
• What phases are shown below?
Agenda 12/7- Cell Cycle and
Mitosis
• Bellwork
• New Information: Cell Cycle and Mitotic
Cell Division (mitosis)
• Lab/Activity: start cell cycle and mitosis
lab- drawings
Cell Cycle and Cell Division
(Mitosis)
• What is mitosis? Why is it important?
Cell Division
• 3 reasons for mitotic cell division (mitosis):
– Growth
– Repair
– Replacement
• Parent cell divides into two identical
daughter cells
Cell Division
• Cells divide to make new cells- DNA is
replicated so each daughter cell gets an
exact copy.
• DNA condenses into chromosomes during
mitosis.
Cell Division
• Humans have 46 chromosomes, 23 from
each parent.
• Haploid cells: only one of each
chromosome (n)
• Diploid cells: two of each chromosome
(2n)
Cell Cycle (click for video clip)
G1 phase
M phase
S phase
G2 phase
Interphase- longest
• G1 Phase
• Cell growth
• S Phase
• DNA replication
• G2 Phase
• preparation for mitosis
•M Phase
• mitosis and cytokinesis
Allium
G1
M phase
S
G2
Interphase
• Nucleus and nuclear envelope are visible.
• One or more nucleoli are visible.
• The rest of the nucleus is filled with
chromatin.
Figure 10-5
Interphase
Prophase
Cytokinesis
Telophase
Metaphase
Anaphase
Prophase
pro- = first; first stage of mitosis
• Nuclear envelope breaks down
• Chromatin condenses into chromosomes
• Centrioles move to opposite poles of the cell
• Spindle fibers attach to chromosomes at the
centromere.
Metaphase
• Chromosome line up in the Middle of the cell
• Chromosome centromeres are attached to the
spindle at the poles of the cell
Anaphase
• Chromosome centromeres separate and sister
chromatids move Apart to the opposite ends of the
cell
Telophase
• Chromosomes precipitate back into strands of
DNA (chromatin)
• A new nuclear envelope begins to form around
each of the two new clumps of DNA
Cytokinesis
(“cell splitting”)
• Same time as Telophase
• Animal Cells:
• cytoplasm splits as the cell membrane draws
inward (cleavage furrow) and splits the cell in two
• Plant Cells:
• cytoplasm splits as a cell plate forms between the
two new nuclei, then a new cell membrane
Cell Cycle and Mitosis
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Protect
Mothers
And
Their
Children
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Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Cell Cycle and Mitosis Virtual Lab
• Go to
http://www.biology.arizona.edu/cell_bio/act
ivities/cell_cycle/cell_cycle.html
• Make a table like the one you’ll see before
the activity begins.
• Answer the following questions:
– Which phase of the cell cycle is longest? How
do you know? Which is shortest, and how do
you know?
Agenda 12/8- Cell Cycle and
Cancer
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Bellwork
Notes- Cell Cycle Control and Cancer
Lab- Mitosis in Onion Root Tip Cells
HW- finish lab questions, study for test
(Thurs)- DNA structure and replication, cell
cycle, and mitosis
Binary Fission
• Prokaryotes (bacteria) reproduce by a type
of cell division called binary fission.
• In binary fission the single bacterial
chromosome replicates and the two
daughter chromosomes actively move
apart.
G1 phase
M phase
S phase
G2 phase
The Cell Cycle Control System
• The events of the cell cycle are directed by a
cell cycle control system, similar to a clock.
G1 checkpoint
Control
system
G1
M
M checkpoint
Figure 12.14
G2 checkpoint
G2
S
The Cell Cycle Control System
• There are specific checkpoints where the cell
cycle stops until a go-ahead signal is received.
G0
G1 checkpoint
G1
G1
Figure 12.15 A, B
(a) If a cell receives a go-ahead
signal at the G1 checkpoint, the
cell continues on in the cell cycle.
(b) If
a cell does not receive a goahead signal at the G1checkpoint,
the cell exits the cell cycle and goes
into G0, a non-dividing state.
Control of Cell Division
• In density-dependent inhibition crowded cells
stop dividing.
• Most animal cells also exhibit anchorage
dependence in which they must be attached to a
substratum to divide.
(a) Normal mammalian cells. The
availability of nutrients, growth
factors, and a substratum for
attachment limits cell
density to a single layer.
Cells anchor to dish surface and
divide (anchorage dependence).
When cells have formed a complete single layer, they
stop dividing
(density-dependent inhibition).
If some cells are scraped away, the remaining cells
divide to fill the gap and then stop (density-dependent
inhibition).
Figure 12.18 A
25 µm
Control of Cell Division
• Cancer cells: no density-dependent inhibition or
anchorage dependence.
• Do not respond normally to the body’s control
mechanisms and form tumors.
• Loss of the cell cycle controls.
Cancer cells do not exhibit
anchorage dependence or
density-dependent inhibition.
(b) Cancer cells. Cancer cells usually
continue to divide well beyond a
single layer, forming a clump of
overlapping cells.
Figure 12.18 B
25 µm
Control of Cell Division
• Malignant tumors invade surrounding tissues
and can metastasize, exporting cancer cells to
other parts of the body where they may form
secondary tumors.
Cancer Risk Factors Quiz
• http://www.webmd.com/cancer/rm-quizcancer-myths-facts
Lab Objectives
• To list the phases of the cell cycle in the order in
which they occur.
• To list the phases of the M-phase of the cell cycle
(Mitosis) and explain what happens during each.
• To illustrate/draw what happens during each phase
of Mitosis.
• To identify the role of cell structures during cell
division (centrioles, chromatin, chromosomes,
nucleus).
• To learn the importance of cell division for
organisms (asexual reproduction, growth, repair).
Mitosis in Allium Root
Interphase
Prophase
Metaphase
Mitosis in Allium Root
Anaphase
Telophase
Prophas
e
Telophase
Interphase
Metaphase
Anaphase
Eukaryotic Cell Division
• Mitosis- normal cell division
– Parent cell divides into two identical daughter
cells (diploid = 2n)
• n = number of types of chromosomes
• Meiosis- cell division resulting in
reproductive cells (gametes)
– Parent cell divides into 4 daughter cells, each
with half the number of chromosomes (haploid
= 1n)
Agenda 12/9- Sexual vs. Asexual
Reproduction
• Discuss lab, finish
• New information: Sexual vs. Asexual
Reproduction
• Activity: Cell Cycle, Mitosis Review
Worksheet
• Quiz tomorrow, Cancer Brochure Research
Project due Monday
Agenda 12/11- Cell Division and
Reproduction
• Bellwork- none
• Types of Cell Division and Reproduction
• Pros/Cons of Sexual vs. Asexual
Reproduction
• Video- Life’s Greatest Miracle
Mitosis
• 2 diploid daughter cells formed, just like
parent cell (two of each chromosome)
• Preceded by interphase (G1, S, G2 phase)
• Mitosis:
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Prophase
Metaphase
Anaphase
Telophase
Figure 10-5
Interphase
Prophase
Cytokinesis
Telophase
Metaphase
Anaphase
Why don’t you look exactly like
your parents or siblings?
• A different form of cell division: Meiosis!
• Sexual reproduction increases genetic
variation in a population, which increases a
species’ ability to adapt to changes in their
environment.
Sexual Reproduction
• Male gamete (sperm) and female gamete
(egg) are haploid (1n)
• Fertilization occurs when an egg and a
sperm fuse to form a zygote (2n).
• Meiosis is the form of cell division that
results in gametes.
Meiosis
occurs in somatic cells to produce reproductive cells
• 4 haploid daughter cells formed (only one of
each chromosome)
• Preceded by interphase and DNA replication
• Two Divisions:
– Meiosis I
– Meiosis II
Why Sex?
The Evolution of Sexual Reproduction
Asexual Reproduction
• offspring are identical to parents
• little variety in population
Sexual Reproduction
• offspring are a combination of parents
• introduces variety in population
The Evolution of Sexual Reproduction
The Red Queen Hypothesis
The Evolution of Sexual Reproduction
The leading hypothesis for why sexual
reproduction has persisted
Refers to Lewis Carroll’s Through the
Looking Glass
The Red Queen says to Alice:
“It takes all the running you can do,
to stay in the same place.”
The Red Queen Hypothesis
The Evolution of Sexual Reproduction
The Red Queen Hypothesis:
As species that live at each other's expense co-evolve,
they are engaged in a constant evolutionary struggle for
a survival advantage. They need "all the running they
can do" because the landscape around them is
constantly changing. (predator/prey, disease/host)
In other words, hosts change the locks, and parasites,
etc invent new keys.
Sexual reproduction is necessary to fight
disease, avoid predation, get food, etc.
Why Sex?
Advantages and Disadvantages of Asexual Reproduction
Sexual Reproduction
Advantages:
 Variation
 More rapid rate of adaptation in
a changing environment
Disadvantages:
 Costs of mating behavior:
competition, no mating
 Only pass on half your genes
Asexual Reproduction
Advantages:
 Pass on all of your genes
 No mating behavior costs (don’t
have to spend time or energy looking
for a mate, no energy wasted on
showy displays)
Disadvantages:
 Little or no variation
 More susceptible to parasites,
viruses, etc.
http://www.pbs.org/wgbh/evolution/library/01/5/l_015_03.html
Costs of Sexual Reproduction:
Displays, Competition for Mates
Life’s Greatest Miracle
• Video with worksheet.
• Answer all questions- classwork grade.