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 chromosomesChromosome: 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
46Chromosomes 92
Chromosomes
2nd Duplicates DNA
3rd Prepares to divide
Clicker Question #1
Which of the following is NOT a reason cells divide?
a.To heal injuriesb.To allow the organism to growc.To reproduced.To maintain homeostasis
Clicker Question #2
What will happen if the cell continued to grow rather than
divide?
a.The organism would get too bigb.Food & wastes would not be able to move in & out as easilyc.The surface area would increase and allow more materials into and out of the celld.Nothing would happen
Clicker Question #3
What are the 3 stages of the cell cycle?
a.Prophase, Metaphase, & Anaphaseb.Mitosis, Telophase, & Cytokinesisc.Interphase, Metaphase, & Prophased.Interphase, Mitosis, & Cytokinesis
Clicker Question #4
Which of the following is NOT a stage during interphase?
a.Growth (G1)b.DNA replicates (S)c.Prepares to divide (G2)d.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 cellsb. 2 genetically identical cellsc. 4 genetically different cellsd. 2 genetically different cells
Clicker Question #6
What are the 4 stages of mitosis in order?
a. Interphase, prophase, metaphase, anaphaseb. Interphase, prophase, metaphase, telophasec. Prophase, metaphase, telophase, cytokinesisd. 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. Cytokinesisb. Interphasec. Telophased. 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
How many chromosomes do we have in each of our body cells (not sex
cells)?
Does more chromosomes an organism has mean that it is
more advanced/smarter?
Humans have 46 in our body cells
What are “body cells”?Brain cells Eye cells
Heart cells Tongue cells
Skin cells Muscle cells
Blood cells Lung cells
Kidney cells Nerve cells
Everything EXCEPT
GAMETES!
No…example:
King Crabs have 208 chromosomes in each cell
No…example:
Turkeys have 82 chromosomes in each cell
What is the difference between
gametes & body cells?
Body cells reproduce using mitosis.
Start with 1 diploid
End with 2 diploid
Notice that they are IDENTICAL!
What is the difference between diploid and
haploid?Diploid – Having two copies of each chromosomes (2n)
Body cells are Diploid
Humans have 46Fruit flies have 8Skunks have 50
If you see Diploid…
You think DOUBLE!
Diploid Video
What is the difference between diploid and
haploid?Haploid – Cell with half the number of chromosomes (n)
Gametes are Haploid
Humans have 23 (in sex cells)
Remember: Humans have 46 (in body cells)
Fruit flies have 4 (in sex cells)
Remember: Fruit Flies have 8 in body cells
Skunks have 25 (in sex cells)
Remember: Skunks have 50 in body cells
If you see haploid…
You think HALF!
23
23
23
23
Haploid Video
Clicker Question #8
Sperm and eggs are:
a. gametesb. somatic cellsc. body cellsd. all of the above
Clicker Question #9
How many chromosomes are in human gametes?
a. 36b. 23c. 20d. 15
Clicker Question #10
Which of the following is an example of a haploid cell?
a. brain cellb. skin cellc. heart celld. sperm cell
Clicker Question #11
Mitosis results in:a. 2 diploid cellsb. 2 haploid cellsc. 4 diploid cellsd. 4 haploid cells
Gametes are formed using meiosis
Notice that they are NOT IDENTICAL
Starts with 1 diploid
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
* Solve math problems better than you
* Fix things better than you
* Sing better than you
* Fly airplanes better than you* Swim better than you
* “Look better” than you
* Paint better than you
* Train animals better than you * Farm better than you
* Dance better than you
* Jump better than you
Crossing-Over Continued…
The same crossing-over patterns do not occur…they create all different kinds of combinations…often called “recombination”…this
makes us genetically unique.
Crossing-over occurs between homologous chromosomes.
Being genetically unique creates genetic diversity!
…diversity is GOOOOD!
Homo means ___?
Homologous Chromosomes means that they contain the SAME genes, in the SAME order as each other, but the message in the genes may be slightly different between the two.
- So your mom’s code could be for blue eyes
- And your dad’s code could be for brown
SAMEGenetic diversity allows some
individuals of the same species to continue as their environment
changes…even if others can’t survive.
Hypothetical….lets say you are a duck…
And shaking your tail feathers will help you find a mate…
cuz that is what the ladyz are look’n for
Then this is the duck that will pass on his genes!
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…BUTMeiosis I
Meiosis II
The DNA does NOT copy before dividing
&
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. skin cellsb. liver cellsc. egg cellsd. kidney cells
Clicker Question #13
Which of the following cells are formed during mitosis?
a. skin cellsb. sperm cellsc. egg cellsd. all of the above
Clicker Question #14
Meiosis results in:a. 2 identical haploid cellsb. 4 identical haploid cellsc. 4 different haploid cellsd. 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. identical twinsb. cloning c. genetic variation d. biodiversity
Clicker Question #16
The exchange of chromosomal segments during meiosis is called:
a. interphaseb. crossing-overc. transcriptiond. exchanging-over
Clicker Question #17
Which of the following allows for genetic diversity?a. meiosisb. mitosisc. homeostasisd. 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.
These are correct!
No problemNotice there are
NO chromosomes in these cells!Notice that
non-disjunction occurred here too!
This is how Down Syndrome happens…the chromosomes don’t separate correctly, and too many
end up in the gamete.
People with Down Syndrome have 47 chromosomes instead of ____.46
Click on Link for animation…
Meiosis Overview
Compare & Contrast Mitosis & Meiosis
Mitosis Meiosis
Both* Occurs in body cells * Occurs in gametes cells
* Creates 2 cells * Creates 4 cells
* Are genetically identical * Are NOT genetically identical
* Creation of new cells
* Increases genetic diversity
* DNA replicates
once
* Divides twice (meiosis 1 & II* Divides once
Page 34 in Comp Book
Clicker Question #18
This results in gametes with abnormal numbers of
chromosomes: a. meiosisb. mitosisc. non-disjunctiond. crossing-over
Clicker Question #19
This is an example of non-disjunction:
a. Color blindnessb. Down Syndromec. Cystic fibrosisd. 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?
Advantages DisadvantagesCan reproduce without a
partner…They don’t have to find a
mate/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.
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
Asexual Reproduction
What are the advantages & disadvantages to being asexual
& sexual?
Advantages DisadvantagesGenetic 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
Sexual Reproduction
Clicker Question #20
Prokaryotes reproduce using:
a. meiosisb. mitosisc. binary fissiond. binary fusion
Clicker Question #21
Which of the following is an advantage of asexual
reproduction a. genetic diversityb. the ability to reproduce quicklyc. the ability to adapt to new habitatsd. slow reproduction
Clicker Question #22
Which of the following is an advantage of sexual
reproduction a. genetic diversityb. the ability to reproduce quicklyc. the ability to reproduce many offspringd. do not have to find a sexual partner
The End
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