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Unit 5
Mitosis & Meiosis
Why do cells divide rather than grow bigger?
– Have you ever been in a traffic jam in a small town?
– Where are major traffic jams found?
• As a city’s population grows, more people are
moving in an out which causes traffic
• Cells are like cities
– The bigger they are, the more food, water, and waste
that must move in and out to keep the cell alive.
Why do cells divide rather than grow bigger?
• To prevent traffic jams, they will divide
• Cells divide for 4 major reasons:
1. Prevent the cell from becoming too big (prevent traffic jam)
2. To heal injuries
3. To allow the organism to grow (up)
4. To reproduce (new individuals)
Before we get started with the cell cycle….
Lets talk about chromosomes
Chromosome: DNA-containing structure that
carries genetic material from one generation to
another.
What happens during the cell cycle?
Cell Cycle - Process of cellular reproduction,
occurring in the main stages
1. Interphase (growth)
2. Mitosis (nuclear division)
3. Cytokinesis (cytoplasm division)
What occurs during Interphase
(the 1st step in cell cycle)
• There are 3 stages during interphase:
1st Grows
2nd Duplicates DNA
46
Chromosomes
3rd Prepares to divide
92
Chromosomes
Clicker Question #1
Which of the following is NOT a reason cells
divide?
a. To heal injuries
b. To allow the organism to grow
c. To reproduce
d. To maintain homeostasis
Clicker Question #2
What will happen if the cell continued to grow
rather than divide?
a.
b.
c.
d.
The organism would get too big
Food & wastes would not be able to move in & out as easily
The surface area would increase and allow more materials into
and out of the cell
Nothing would happen
Clicker Question #3
What are the 3 stages of the cell cycle?
a.
b.
c.
d.
Prophase, Metaphase, & Anaphase
Mitosis, Telophase, & Cytokinesis
Interphase, Metaphase, & Prophase
Interphase, Mitosis, & Cytokinesis
Clicker Question #4
Which of the following is NOT a stage
during interphase?
a.
b.
c.
d.
Growth (G1)
DNA replicates (S)
Prepares to divide (G2)
Mitosis (M)
What is Mitosis?
Mitosis:
2nd main stage of the cell cycle during
which the cell’s replicated DNA divides and 2
genetically identical diploid daughter cells are
produced.
What occurs during mitosis?
(the 2nd step in cell cycle)
• There are 4 stages during mitosis:
1st Prophase (pro = 1st)
2nd Metaphase
3rd Anaphase
4th Telophase (telo = end)
What occurs during mitosis?
(the 2nd step in cell cycle)
• There are 4 stages during mitosis:
1st Prophase (pro = 1st)
Nucleus disappears
Centrioles separate
What occurs during mitosis?
(the 2nd step in cell cycle)
• There are 4 stages during mitosis:
2nd Metaphase
Chromosomes line up in
the middle
What occurs during mitosis?
(the 2nd step in cell cycle)
• There are 4 stages during mitosis:
3rd Anaphase
Chromosomes move apart
What occurs during mitosis?
(the 2nd step in cell cycle)
• There are 4 stages during mitosis:
4th Telophase (telo = end)
Nucleus reappears
Cytoplasm starts to
separate
What occurs during cytokinesis?
(the 3rd step (LAST) in cell cycle)
• Cytokinesis: The last stage of the cell cycle,
during which the cell’s cytoplasm divides,
creating a new cell.
Daughter Cells
Clicker Question #5
Mitosis creates:
a. 4 genetically identical cells
b. 2 genetically identical cells
c. 4 genetically different cells
d. 2 genetically different cells
Clicker Question #6
What are the 4 stages of mitosis in order?
a. Interphase, prophase, metaphase, anaphase
b. Interphase, prophase, metaphase, telophase
c. Prophase, metaphase, telophase, cytokinesis
d. Prophase, metaphase, anaphase, telophase
Clicker Question #7
This is the last phase of the cell cycle where the
cell’s cytoplasm divides to create 2 daughter cells:
a. Cytokinesis
b. Interphase
c. Telophase
d. Metaphase
Now,
lets look at the
difference between
gametes & body cells.
What is the difference between
gametes & body cells?
Gametes – A haploid sex cell, formed during
meiosis, that can combine with another haploid sex
cell and produce a diploid fertilized egg.
Sperm & Egg
are gametes!
How many chromosomes
are in human gametes?
23
What is the difference between
gametes & body cells?
Does
more are
chromosomes
an organism
What
“body cells”?
Brain cells
cells it isEverything
has meanEyethat
more EXCEPT
Heart cells advanced/smarter?
Tongue cells
GAMETES!
Skin cells
Muscle cells
Blood cells
Lung cells
Kidney cells
Nerve cells
How
many chromosomes do we have in each of
No…example:
our body cells (not sex cells)?
46
King
Crabs
have
208
chromosomes
in
each
cell
Turkeys
have
82
chromosomes
in
each
cell
Humans have
in our body cells
Body cells reproduce using mitosis.
Start with 1 diploid
Notice that they are IDENTICAL!
End with 2 diploid
What is the difference between
diploid and haploid?
Diploid – Having two copies of each chromosomes (2n)
Body cells are Diploid
If you see Diploid…
Fruit
flies have
have
Skunks
Humans
have 850
46
You think DOUBLE!
Diploid Video
What is the difference between
diploid and haploid?
Haploid – Cell with half the number of chromosomes (n)
23
23
23
Gametes are Haploid
23
If you see haploid…
Humans
have
23
sex
cells)
Fruit flies
have
4 (in
(insex
sex
cells)
Skunks
have
25(in
cells)
Remember:
have
46
body
Remember:
Skunks
have
508(in
ininbody
cells
Remember:Humans
Fruit Flies
have
bodycells)
cells
You think HALF!
Haploid Video
Clicker Question #8
Sperm and eggs are:
a. gametes
b. somatic cells
c. body cells
d. all of the above
Clicker Question #9
How many chromosomes are in
human gametes?
a.
b.
c.
d.
36
23
20
15
Clicker Question #10
Which of the following is an example
of a haploid cell?
a.
b.
c.
d.
brain cell
skin cell
heart cell
sperm cell
Clicker Question #11
Mitosis results in:
a.
b.
c.
d.
2 diploid cells
2 haploid cells
4 diploid cells
4 haploid cells
Gametes are formed using meiosis
Starts with 1 diploid
Notice that they are
NOT IDENTICAL
Ends with 4 DIFFERENT haploid
What happens during Meiosis?
Meiosis:
Reduction division process, occurring only in
reproductive cells, in which 1 diploid (2n) cells produce
4 haploid (n) cells that are NOT genetically identical.
Creates SPERM inside
the testes of males
Creates EGGS inside
the ovaries of females
What happens during Meiosis?
There are 2 stages during Meiosis:
Meiosis I & Meiosis II
Meiosis I is exactly like mitosis EXCEPT that
Crossing-over occurs during prophase I
What happens during Meiosis?
Crossing-over:
Exchange of chromosomal segments
between a pair of homologous chromosomes during
prophase I of meiosis
Meiosis I
Meiosis II
Why is crossing-over so important? (cuz it is)
• It creates genetic variation!
• Even though you look similar to your siblings (if same parents),
there will never be another person exactly like you because of
crossing-over…your parents could have a million kids, and not
one of them will look exactly like you!
(except for identical twins, but even they have some differences)
Genetic variation allows some individuals to:
* Run faster than you
* Fix things better than you
* Solve math problems better than you
* Train animals better than you
* Fly airplanes better than you
* Swim better than you
* “Look better” than you
* Paint better than you
* Sing better than you
* Farm better than you
* Dance better than you
* Jump better than you
Crossing-Over Continued…
Crossing-over occurs between
homologous chromosomes.
Homo
means
___?
The same crossing-over patterns do
SAME
not occur…they create all different
kinds
of they
combinations…often
Homologous Chromosomes means
that
contain the SAME
Being
genetically unique called
“recombination”…this
genes, in the SAME order as each
other,
but the message in the
creates
genetic
diversity!
makes usthe
genetically
unique.
genes may
be slightly
different between
two.
…diversity
GOOOOD!
- Soisyour
mom’s code could be for blue eyes
Genetic diversity allows some
And
yourspecies
dad’stocode
individuals- of
the same
continue as their environment
changes…even if others can’t survive.
could be for brown
Hypothetical….lets say you are a duck…
And shaking your tail feathers will
Then this is the duck that
help you find a mate…
will pass on his genes!
cuz that is what the ladyz are look’n for
Hypothetical…lets say you are a caveman
Which of these would
be LESS likely to
survive?
Because all these cave people have
genetic diversity, but one lacks an
important trait (ability to build tools), he
will not survive his environment…
but the others will!
What happens during Meiosis?
Next is Meiosis II….
* The division process happens again…BUT
Meiosis I
The DNA does NOT copy
before dividing
&
Meiosis II
No crossing-over
Results in 4 haploid cells that are NOT identical
Clicker Question #12
Which of the following cells are
formed during meiosis?
a.
b.
c.
d.
skin cells
liver cells
egg cells
kidney cells
Clicker Question #13
Which of the following cells are
formed during mitosis?
a.
b.
c.
d.
skin cells
sperm cells
egg cells
all of the above
Clicker Question #14
Meiosis results in:
a.
b.
c.
d.
2 identical haploid cells
4 identical haploid cells
4 different haploid cells
2 different haploid cells
Clicker Question #15
This allows some individuals of the same species to
continue as their environment change even if others
can’t survive
a.
b.
c.
d.
identical twins
cloning
genetic variation
biodiversity
Clicker Question #16
The exchange of chromosomal
segments during meiosis is called:
a.
b.
c.
d.
interphase
crossing-over
transcription
exchanging-over
Clicker Question #17
Which of the following allows for
genetic diversity?
a.
b.
c.
d.
meiosis
mitosis
homeostasis
all of the above
Houston…We have a problem…
Non-disjunction: Cell division in which
the sister chromatids do NOT separate
correctly, resulting in gametes with an
abnormal number of chromosomes.
This is how Down Syndrome
These
are
correct!
happens…the chromosomes don’t
Noticeand
there
are
separate correctly,
too
many
No problem
end up
in the
gamete.
NO
chromosomes
in Notice
thesethat
cells!
People with Down Syndrome have
non-disjunction occurred
47 chromosomes instead of ____.
46
here too!
Click on Link for animation…
Meiosis Overview
Compare & Contrast Mitosis & Meiosis
Mitosis
* Occurs in body cells
* Divides once
* Creates 2 cells
* Are genetically identical
Meiosis
Both
* Creation of
new cells
* Occurs in gametes cells
* Divides twice (meiosis 1 & II
* Creates 4 cells
* DNA
replicates
once
* Are NOT genetically identical
* Increases genetic diversity
Clicker Question #18
This results in gametes with
abnormal numbers of chromosomes:
a.
b.
c.
d.
meiosis
mitosis
non-disjunction
crossing-over
Clicker Question #19
This is an example of nondisjunction:
a.
b.
c.
d.
Color blindness
Down Syndrome
Cystic fibrosis
Sickle cell anemia
Many Bacteria & protozoans do not need a partner
to reproduce. Are they reproducing using mitosis?
Answer: NO...They are using Binary Fission
Binary Fission – Asexual form of reproduction used
by some prokaryotes in which a cell divides into two
genetically identical cells. (creates a new individual)
SIMILAR/LIKE “cloning” themselves
1 bacterium could become 1,000,000,000 (billion) in 10 hours!
What are the advantages &
disadvantages to being asexual & sexual?
Asexual Reproduction
Advantages
Disadvantages
Can reproduce without a partner…
No genetic variation…They are clones.
Its putting all your eggs in one basket.
If a something kills the parent, it
WILL kill ALL the offspring too.
Easily becomes extinct with little
change to environment.
They don’t have to find a mate/partner.
Able to reproduce quickly. The greater
the number of offspring, the better the
survival rate of the population.
Quick reproduction is also a
disadvantage because too many
individuals will be competing with each
other for food & space
What are the advantages &
disadvantages to being asexual & sexual?
Sexual Reproduction
Advantages
Disadvantages
Genetic diversity!
Has the ability to create endless
recombination of genes (crossing-over)
coming from 2 parents, all individuals are
different in some way.
Must find a partner. Very difficult if
the population is low and spread out.
Difficult to recover if the species is
endangered.
The species is more able to adapt to
environmental changes
Slow reproduction….takes time…
Slow population growth
Clicker Question #20
Prokaryotes reproduce using:
a.
b.
c.
d.
meiosis
mitosis
binary fission
binary fusion
Clicker Question #21
Which of the following is an
advantage of asexual reproduction
a.
b.
c.
d.
genetic diversity
the ability to reproduce quickly
the ability to adapt to new habitats
slow reproduction
Clicker Question #22
Which of the following is an advantage of
sexual reproduction
a.
b.
c.
d.
genetic diversity
the ability to reproduce quickly
the ability to reproduce many offspring
do not have to find a sexual partner
The End