Download Meiosis

Copyright © 2010 Ryan P. Murphy
• Keep an eye out for “The-Owl” and raise
your hand as soon as you see him.
– He will be hiding somewhere in the slideshow
Copyright © 2010 Ryan P. Murphy
• Keep an eye out for “The-Owl” and raise
your hand as soon as you see him.
– He will be hiding somewhere in the slideshow
“Hoot, Hoot”
“Good Luck!”
Copyright © 2010 Ryan P. Murphy

New Area of Focus: Meiosis and Genetics
Copyright © 2010 Ryan P. Murphy
• We’ve learned mitosis, now lets learn
Meiosis. Very similar except for a few steps.
Copyright © 2010 Ryan P. Murphy

Mitosis is 99.9% of your bodies cells.
Copyright © 2010 Ryan P. Murphy
Mitosis is 99.9% of your bodies cells.
 Meiosis is just your sex cells.

Copyright © 2010 Ryan P. Murphy
• Video Link! Differences between mitosis and
meiosis.
– Pay attention as you will need to tell me the
difference at the end.
– http://www.youtube.com/watch?v=Ba9LXKH2ztU
&feature=related
Stages of Meiosis
• Meiosis is a form of cell division that
produces daughter cells with half the
number of chromosomes that are in the
parent cell.
• During meiosis, a diploid cell goes through
two divisions to form four haploid cells.
• In meiosis I, homologous chromosomes
are separated. In meiosis II, the sister
chromatids of each homologue are
separated.
Copyright © 2010 Ryan P. Murphy
Copyright © 2010 Ryan P. Murphy
Copyright © 2010 Ryan P. Murphy
Copyright © 2010 Ryan P. Murphy
Copyright © 2010 Ryan P. Murphy
Copyright © 2010 Ryan P. Murphy
• Which type of cells does Meiosis occur in?
Copyright © 2010 Ryan P. Murphy
• Sex Cells: The sperm (male), Egg
(Female)
• All of the cells in our body except for our
sex cells have 46 chromosomes.
• All of the cells in our body except for our
sex cells have 46 chromosomes.
• Our sex cells have 23. Why?
• Answer: Because our sex cells (23) are
the sperm and the egg.
Copyright © 2010 Ryan P. Murphy
• Answer: Because our sex cells (23) are
the sperm and the egg. When sperm (23)
and egg (23) meet, you get the correct
number of human chromosomes of 46.
Copyright © 2010 Ryan P. Murphy
• Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– Brain cell
– Muscle cell
– Egg Cell
– Liver cell
– Heart cell
– Nerve cell
– Skin cell
– Sperm cell
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Sex Cells (Haploid)
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Sex Cells (Haploid)
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Sex Cells (Haploid)
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Sex Cells (Haploid)
23
23
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Sex Cells (Haploid)
46
Copyright © 2010 Ryan P. Murphy
• Answer! Who was paying attention.
• Name the number of chromosomes in each
human cells below?
– 46 Brain cell
– 46 Muscle cell
– 23 Egg Cell
– 46 Liver cell
– 46 Heart cell
– 46 Nerve cell
– 46 Skin cell
– 23 Sperm cell
Sex Cells (Haploid)
Diploid
46
Copyright © 2010 Ryan P. Murphy

Meiosis: Cell division that produces
reproductive cells.
Copyright © 2010 Ryan P. Murphy
Meiosis I
 Meiosis begins with a diploid cell that has
copied its chromosomes.
 During prophase I, the chromosomes
condense, and the nuclear envelope
breaks down. Homologous chromosomes
pair. Chromatids exchange genetic
material in a process called crossing-over.

In metaphase I, the spindle moves the pairs of
homologous chromosomes to the equator of the cell.
The homologous chromosomes remain together.
In anaphase I, the homologous chromosomes separate.
The spindle fibers pull the chromosomes of each pair to
opposite poles of the cell. But the chromatids do not
separate at their centromeres. Each chromosome is still
made of two chromatids. The genetic material, however,
has recombined.

During telophase I, the cytoplasm divides
(cytokinesis), and two new cells are
formed. Both cells have one chromosome
from each pair of homologous
chromosomes.

Meiosis…
-
Copyright © 2010 Ryan P. Murphy

Meiosis…
 -Has
two cell divisions.
-
Copyright © 2010 Ryan P. Murphy

Meiosis…
 -Has
two cell divisions.
 -A reduction in the amount of genetic material.
-
Copyright © 2010 Ryan P. Murphy

Meiosis…
 -Has
two cell divisions.
 -A reduction in the amount of genetic material.
 -Results
in half the number of chromosomes.
Copyright © 2010 Ryan P. Murphy
• Meiosis…
– Has two cell divisions.
– A reduction in the amount of genetic material
• Results in half the number of chromosomes.
First
Division
Copyright © 2010 Ryan P. Murphy
Meiosis II
• Meiosis II begins with the two cells formed
at the end of telophase I of meiosis I.
• The chromosomes are not copied between
meiosis I and meiosis II.
• In prophase II, new spindles form.
• During metaphase II, the chromosomes
line up along the equators and are
attached at their centromeres to spindle
fibers.
• In anaphase II, the centromeres divide.
The chromatids, which are now called
chromosomes, move to opposite poles of
the cell.
• During telophase II, a nuclear envelope
forms around each set of chromosomes.
The spindle breaks down, and the cell
goes through cytokinesis.
• The result of meiosis is four haploid cells.
• Meiosis…
– Has two cell divisions.
– A reduction in the amount of genetic material
• Results in half the number of chromosomes.
First
Division
Second
Division
Copyright © 2010 Ryan P. Murphy
• Meiosis…
– Has two cell divisions.
– A reduction in the amount of genetic material
• Results in half the number of chromosomes.
Copyright © 2010 Ryan P. Murphy
• Meiosis…
– Has two cell divisions.
– A reduction in the amount of genetic material
• Results in half the number of chromosomes.
Divided in half
Copyright © 2010 Ryan P. Murphy
• Meiosis…
– Has two cell divisions.
– A reduction in the amount of genetic material
• Results in half the number of chromosomes.
Divided in half
Copyright © 2010 Ryan P. Murphy
• Meiosis…
– Has two cell divisions.
– A reduction in the amount of genetic material
• Results in half the number of chromosomes.
Divided in half
No Replication
Copyright © 2010 Ryan P. Murphy
• Meiosis…
– Has two cell divisions.
– A reduction in the amount of genetic material
• Results in half the number of chromosomes.
Divided in half
No Replication
Copyright © 2010 Ryan P. Murphy
• Meiosis…
– Has two cell divisions.
– A reduction in the amount of genetic material
• Results in half the number of chromosomes.
Reduction
of genetic
material
Divided in half
No Replication
Copyright © 2010 Ryan P. Murphy
• Meiosis…
– Has two cell divisions.
– A reduction in the amount of genetic material
• Results in half the number of chromosomes.
Reduction
of genetic
material
Divided in half
No Replication
Copyright © 2010 Ryan P. Murphy
Comparing Mitosis and
Meiosis
• The processes of mitosis and meiosis are
similar but meet different needs and have
different results.
• Mitosis makes new cells that are used
during growth, development, repair, and
asexual reproduction.
• Meiosis makes cells that enable an
organism to reproduce sexually and
happens only in reproductive structures.
• Time to learn about the birds and the bees
/ Sex Ed.
Copyright © 2010 Ryan P. Murphy
• Disclaimer! Caution the next slide is of adult
content, please be advised about this before
you view!
Copyright © 2010 Ryan P. Murphy
Caution!
Copyright © 2010 Ryan P. Murphy
Caution!
Copyright © 2010 Ryan P. Murphy
Copyright © 2010 Ryan P. Murphy
Copyright © 2010 Ryan P. Murphy
Copyright © 2010 Ryan P. Murphy
Copyright © 2010 Ryan P. Murphy
Copyright © 2010 Ryan P. Murphy
Copyright © 2010 Ryan P. Murphy
Copyright © 2010 Ryan P. Murphy
• Blastocyst formation after fertilization
Copyright © 2010 Ryan P. Murphy
Sperm has 23 chromosomes (haploid)
 Egg has 23 chromosomes (haploid)

 When
they meet you have 46 (diploid)
Copyright © 2010 Ryan P. Murphy
Sperm has 23 chromosomes (haploid)
 Egg has 23 chromosomes (haploid)

 When
they meet you have 46 (diploid)
Copyright © 2010 Ryan P. Murphy
Sperm has 23 chromosomes (haploid)
 Egg has 23 chromosomes (haploid)

 When
they meet you have 46 (diploid)
Copyright © 2010 Ryan P. Murphy
Sperm has 23 chromosomes (haploid)
 Egg has 23 chromosomes (haploid)

 When
they meet you have 46 (diploid)
Copyright © 2010 Ryan P. Murphy
• Why don’t you look exactly like your brother
or sister? If same parents.
Copyright © 2010 Ryan P. Murphy
• Why don’t you look exactly like your brother
or sister? If same parents.
Copyright © 2010 Ryan P. Murphy
• Why don’t you look exactly like your brother
or sister? If same parents.
Copyright © 2010 Ryan P. Murphy
• Unless you are an identical twin, your DNA
is unique to only you.
• Answer! There is nobody else like you on
the planet because of some key events
that occur during Meiosis.
Copyright © 2010 Ryan P. Murphy
• Can you find the key events of mitosis in the
animation below?
Copyright © 2010 Ryan P. Murphy
• Video! Meiosis
Copyright © 2010 Ryan P. Murphy
All Different
Which one will
reach the egg?

Crossing Over : Genetic segments of
information are swapped when the
chromosomes are next to each other
(random and creates millions of
possibilities)
Copyright © 2010 Ryan P. Murphy

Crossing Over : Genetic segments of
information are swapped when the
chromosomes are next to each other
(random and creates millions of
possibilities)
Copyright © 2010 Ryan P. Murphy

Crossing Over : Genetic segments of
information are swapped when the
chromosomes are next to each other
(random and creates millions of
possibilities)
Copyright © 2010 Ryan P. Murphy

Crossing Over : Genetic segments of
information are swapped when the
chromosomes are next to each other
(random and creates millions of
possibilities)
Copyright © 2010 Ryan P. Murphy

Therefore, a main difference between
meiosis and mitosis is that in meiosis,
genetic information is rearranged leading
to genetic variation in offspring.
Genetic Variation

Genetic variation is advantageous for a
population.

Genetic variation can help a population
survive a major environmental change.

Genetic variation is made possible by
sexual reproduction
Genetic Variation, continued
In sexual reproduction, existing genes are
rearranged. Meiosis is the process that
makes the rearranging of genes possible.
 Fusion of haploid cells from two different
individuals adds further variation.
 Three key contributions to genetic
variation are crossing-over,
independent assortment, and random
fertilization.


Reduction of genetic information
 Produces
cells).
four different germ (reproductive
Copyright © 2010 Ryan P. Murphy

Reduction of genetic information
 Produces
cells).
four different germ (reproductive
Copyright © 2010 Ryan P. Murphy

Reduction of genetic information
 Produces
cells).
four different germ (reproductive
Copyright © 2010 Ryan P. Murphy

Reduction of genetic information
 Produces
cells).
four different germ (reproductive
Copyright © 2010 Ryan P. Murphy

Reduction of genetic information
 Produces
cells).
four different germ (reproductive
Copyright © 2010 Ryan P. Murphy

Reduction of genetic information
 Produces
cells).
four different germ (reproductive
Copyright © 2010 Ryan P. Murphy

Reduction of genetic information
 Produces
cells).
four different germ (reproductive
Copyright © 2010 Ryan P. Murphy

Reduction of genetic information
 Produces
cells).
four different germ (reproductive
Copyright © 2010 Ryan P. Murphy

Reduction of genetic information
 Produces
cells).
four different germ (reproductive
Which
will
fertilize?
Copyright © 2010 Ryan P. Murphy

Reduction of genetic information
 Produces
cells).
four different germ (reproductive
Which
will
fertilize?
X
Copyright © 2010 Ryan P. Murphy

Reduction of genetic information
 Produces
cells).
four different germ (reproductive
Which
will
fertilize?
X
X
Copyright © 2010 Ryan P. Murphy

Reduction of genetic information
 Produces
cells).
four different germ (reproductive
Which
will
fertilize?
X
X X
Copyright © 2010 Ryan P. Murphy

Reduction of genetic information
 Produces
cells).
four different germ (reproductive
Which
will
fertilize?
X
X X
Copyright © 2010 Ryan P. Murphy
Crossing-over
• During prophase I, homologous
chromosomes line up next to each other.
• Each homologous chromosome is made of
two sister chromatids attached at the
centromere.
• Crossing-over happens when one arm of a
chromatid crosses over the arm of the
other chromatid.
Crossing-over
• The chromosomes break at the point of
the crossover, and each chromatid reforms its full length with the piece from the
other chromosome.
• Thus, the sister chromatids of a
homologous chromosome no longer have
identical genetic information.
Independent Assortment
• During metaphase I, homologous pairs of
chromosomes line up at the equator of the
cell.
• The two pairs of chromosomes can line up
in either of two equally probable ways.
• This random distribution of homologous
chromosomes during meiosis is called
independent assortment.
Random Fertilization
• Fertilization is a random process that adds
genetic variation.
• The zygote that forms is made by the
random joining of two gametes.
• Because fertilization of an egg by a sperm
is random, the number of possible
outcomes is squared.
• Which sperm will fertilize the egg?
– It is usually only one.
A
B
C
D
Copyright © 2010 Ryan P. Murphy
• Answer! It is completely random. This is
what makes you completely unique.
C
Copyright © 2010 Ryan P. Murphy
• Only one of the eggs will become a viable
egg for fertilization.
A
B
C
D
Copyright © 2010 Ryan P. Murphy
• Activity! Simulating Meiosis with the
chromosome beads during video on next
slide.
– Show crossing over.
– Show reduction division.
Copyright © 2010 Ryan P. Murphy
• Video Link! Meiosis
• http://www.youtube.com/watch?v=kVMb4J
s99tA
• Try and figure out the picture under the
boxes.
– Raise your hand when you think you know.
– You only get one guess.
Copyright © 2010 Ryan P. Murphy
Fertilization
Fertilization
Egg
Haploid
Fertilization
Egg
Haploid
Sperm
Haploid
Fertilization
Egg
+
Sperm
Fertilization
Egg
+ Diploid
Sperm
• Try and figure out the picture under the
boxes.
– Raise your hand when you think you know.
– You only get one guess.
Copyright © 2010 Ryan P. Murphy
Copyright © 2010 Ryan P. Murphy