Goal 3.02: Sexual and Asexual Reproduction
Asexual Reproduction
Sexual Reproduction
makes clones
(genetically identical copies)
makes gametes
(genetically different zygotes)
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MITOSIS
MEIOSIS
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MITOSIS
(Asexual Reproduction/Cloning)
1
Parent
Cell
Identical daughter cells
What does this cut have to do with Mitosis?
Why do cells need Mitosis?
• for reproduction
– one celled organisms (clones)
• for growth & development
– from fertilized egg to multicelled organism
• for repair
– replace cells that die or are
lost
Mitosis & Reproduction
• Asexual Reproduction
– Cloning the traits of a
single parent to create a
new organism that is
genetically identical to the
parent
– Advantages
• Don’t have to find a partner
– Disadvantages
• No chance to improve the
species. Why not?
Mitosis & Reproduction (cont.)
• Single-celled eukaryotes
– yeast
– Paramecium
– Amoeba
• Simple multicellular
eukaryotes
“BUD”
– Hydra
• budding
What are the
disadvantages of
asexual reproduction?
What are the
advantages?
Mitosis & The Cell Cycle
G1 = Resting and Growth
S = DNA is replicated
G2 = Growth & Prep
for Mitosis
M = Mitosis
(cell division)
At what point does a normal cell need to divide?
Imagine a cell that is shaped like a cube (like some plant cells).
The surface area increased from 6 to 24 sq mm (x2)
The volume increased from 1 to 8 (x8)
What do you notice about the surface area to volume ratio?
MITOSIS:
Dividing of the DNA -- Dividing of the Cell
http://highered.mcgrawhill.com/sites/0072495855/student_view0/c
hapter2/animation__mitosis_and_cytokines
is.html
Copied & Paired Up Chromosomes
Single DNA strand
centromere
Two new DNA strands linked by centromere
making one doubled chromosome.
Cell Prepares to Divide
chromosomes are duplicated
DNA in chromosomes
4 single-stranded
chromosomes
Centromeres
link
chromosomes
4 duplicated chromosomes
nucleus
duplicated chromosomes
nucleus
NOT MITOSIS…
• S phase of Cell Cycle: DNA Replication
occurs.
DNA
nucleus
(INTERPHASE)
happens BEFORE Mitosis!
Mitosis Begins…
• Stage 1: DNA winds into chromosomes
Pro = first
duplicated chromosomes
nucleus
PROPHASE
…MITOSIS Continues…
• Stage 2: Chromosomes line up in middle
– attached to protein spindle fibers that will pull
them apart.
METAPHASE
Meta = middle
…Mitosis continues….
• Stage 3: Chromosomes separate
Ana = without
– chromosomes split, separating the pairs
– start moving to opposite ends (poles)
ANAPHASE
…Mitosis ends.
Telo= end
• Stage 4:
• Cytokinesis occurs
– cells start to divide
– nucleus forms again
TELOPHASE
What do you have at the end of Mitosis?
• Get 2 exact genetic copies of original cells
– same DNA
– “clones”
Overview of mitosis
Start with 2
chromosomes
in each cell.
End with 2
chromosomes
in each cell.
How many chromosomes
per cell? 2
How many chromosomes
per cell? 2
How many chromosomes? _____
Color each sister
chromatid a
different color.
MITOSIS
How many chromosomes? ___
How many chromosomes? ___
Mitosis in whitefish embryo
Mitosis in plant cell
Anaphase
Mitosis in onion root tip
Bio-Online Cell Cycle & Mitosis
(click link on my website)
Telophase
Metaphase
MEIOSIS
(Sexual Reproduction)
Completely
different daughter
cells.
2
Parent
Cells
What does
meiosis have
to do with
these foals?
An example:
“Daddy Kat”
“Mama Kitty”
www.sbpoet.com
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images.free-extras.com
“Kittens Galore!”
Another example:
“Big Daddy”
“Sweet Mama”
Everyone
46
+ 46 = 92!
knows it takes
two to
make
Not
Good!
babies.
How can we
That’s
get the how
right
we getof
number
variation!
chromosomes
BUT
in
the HOW?
babies?
46 chromosomes
46 chromosomes
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1.bp.blogspot.com
MEIOSIS
92
46 chromosomes!?
chromosomes
46
23
MEIOSIS
23
metropolitician.blogs.com
www.babble.com
OK, you
can only
workhihi11.seesaa.net
with
durtbagz.wordpress.com
Mutant
Baby!
meandvinnie.blogspot.com
www.greatwhatsit.com
what babyinsane.com
you’ve got.
spanishdict.com
The process of making the ½ set of
chromosome units is called…
MEIOSIS
If you’re a plant, you make
pollen and ovules.
If you’re an animal, you make
sperm and eggs.
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www.alvesbio.com
images.mooseyscountrygarden.com
www.flatrock.org.nz
Normal Humans have two
copies of 23 chromosomes
(gives a total of 46
chromosomes).
We refer to this as “Diploid”
and represent it with “2n.”
The testicles and ovaries are
Diploid (2n).
They must create sperm and
eggs that have only one copy
of each chromosome.
Meiosis is how they cut the
chromosome number in half.
How Meiosis Works
2n
46 chromosomes
(23 pairs)
MEIOSIS I & II
MAN
(meiosis has two parts)
testis
End with four haploid 1n sperm!
Telophase I
2n
1n
Telophase II
Prophase I
Metaphase I
Anaphase II
Anaphase I
Metaphase II
MEIOSIS I & II
WOMAN
(meiosis has two parts)
ovary
End with four haploid 1n eggs!
Telophase I
2n
1n
Telophase II
Prophase I
Metaphase I
Anaphase II
Anaphase I
Metaphase II
Meiosis = Reduction Division
• Meiosis
– DIVIDES the cell into 4 new cells.
– Provides VARIATION in the species!
– REDUCE number of chromosomes
• 2n  1n
• diploid  haploid
– half
– makes gametes
• sperm, eggs, pollen, ovules
Putting it all together…
meiosis  fertilization  mitosis + development
Parents
GAMETES
EGG
46
2n
23
MEIOSIS 1n
SPERM
46
23
23
46
46
46
2n 46 46
46 46
23
ZYGOTE
MITOSIS &
development
Meiosis vs Mitosis: http://www.pbs.org/wgbh/nova/miracle/divi_flash.html
MEIOSIS I & II
WORKSHEET: Color each sister chromatid a
different color. Then follow that sister with the
same color as it goes through meiosis.
Telophase I
Prophase I
Telophase II
Metaphase I
Anaphase II
Anaphase I
Metaphase II
Meiosis is the way
nature creates
new individuals.
This is called
genetic variation.
www4.ncsu.edu
mdbfamily.com
www.steveirwinday.org
Genes from the
parents are mixed
at random to make
the offspring.
Offspring of the same two parents may look very similar…
But unless they are identical twins, they are not exactly the same.
Speaking of Twins: Because identical twins develop from a single
zygote, they have the same genome..
Twins: http://health.howstuffworks.com/pregnancy-and-parenting/pregnancy/fetal-development/adam-200116.htm
People living in
malaria-infested
areas have an
advantage if they
have sickle-cell
anemia. Sickled
cells are not
susceptible to
malaria.
SOMETIMES
Fertilization …
For a human female with 23 pairs of
chromosomes (2n=46), there could be
each sperm carries a
unique selection of
chromosomes that mix
with the unique set of
chromosomes in each
egg cell.
Each female has about:
7 million eggs as a fetus
1 million when born
300,000 at puberty
(about 400 will actually mature)
Random Fertilization
So how many
different
possibilities are
there?
8,388,608 genetically different eggs.
For a human male with 23 pairs of
chromosomes (2n = 46),
this number would be 223 or 8,388,608
genetically different sperm.
Each male produces about 1000 sperm/second!
About 1,000,000 sperm enter the uterus.
About 1000 sperm reach the egg.
Crossing-Over
• During Meiosis I, chromosomes exchange
genes through a process called crossing-over.
If crossing over occurs an
average of three times per
meiosis we get
67,108,864
genetically different sperm!
contexo.info
Independent
Assortment of
chromosomes.
There are many,
many ways the
chromosomes
can be
recombined
during meiosis.
This gives us
70,368,744,000,000
Possibilities for each
and every sperm!
Independent Assortment of Chromosomes (play silent with note to letters)
http://www.sumanasinc.com/webcontent/animations/content/independentassortment.html
Because MEIOSIS gives so many different possibilities
for each and every gamete (sperm or egg), it provides
us with a HUGE amount of VARIATION among species.
sowaglawhippets.blogspot.com
Sometimes things go wrong…
Nondisjunction
http://sumanasinc.com/webcontent/animations/content/mistakesmeiosis/mistakesmeio
sis.html
Nondisjunction
Watch this video and try to recognize when something goes wrong.
Nondisjunction
http://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Meiosis%20I.htm
Now let’s watch a video that explains what happens.
When Meiosis goes wrong
http://www.sumanasinc.com/webcontent/animations/content/mistakesmeiosis/mistakesmeiosis.html
OK, You Try It!
Draw the sequence of events when Nondisjunction occurs during
Meiosis I and when it occurs during Meiosis II.
Nondisjunction in
Meiosis _1__
Prophase I
Metaphase I
Example. (You may wish to
cause a different Meiosis I
nondisjunction in your cells.)
Anaphase I
Metaphase II
Metaphase II
-1
Anaphase II
Anaphase II
Telophase II
Telophase II
n
n
n+1
n-1
Klinefelter’s Syndrome
Bio Project: Draw Meiosis with nondisjuntion
that would result in this condition.
Assignment:
Coach Book L16
Study Island Lesson 8
Any
Questions?