Neo/Sci
Student’s Guide
Name
Teacher
Date
Period
Meiosis Simulation
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Objectives
The Stages of Meiosis
Understand the role chromosomes play in the
process of reproduction.
Simulate the phases of Meiosis I and II and the
phenomenon of “Crossing-Over”.
Demonstrate how sexual reproduction produces
genetic diversity.
Compare and contrast the processes of mitosis
and meiosis.
In this laboratory activity, you will use pop beads to
simulate the stages of meiosis. As you read about
each stage, use the diagrams to follow the movement
of the chromosomes.
Background
Meiosis is the first step in the formation of both eggs
and sperm. The word “meiosis” comes from the
Greek word meaning “diminution” or “lessening”.
During meiosis, diploid cells divide to form haploid
cells. Through this process, the number of
chromosomes per cell is reduced to half the original
number. A nucleus in the diploid cell contains two
sets of chromosomes that are very similar to each
other. These two sets are called “homologues”; one
of the two sets comes from the mother and the other
comes from the father. Only one pair of
chromosomes is not necessarily homologous; this
exception is the sex chromosomes. A normal egg or
sperm contains only half the original number of
chromosomes, that is, only one set of chromosomes
instead of the two sets of homologous pairs. Such a
cell is said to be “haploid”.
The combination of a sperm cell and an egg cell,
called “fertilization”, is necessary for the
development of a new organism. After meiosis, each
sex cell contains half the normal number of
chromosomes as the original parent. When sex cells
combine to produce an offspring, each sex cell
contributes half the normal number of chromosomes.
Thus, the new offspring gets the normal number of
chromosomes with half coming from each parent.
MeiosisSimulation.BWG.doc 02/02/12
Interphase I
Before meiosis begins, the DNA in the diploid
nucleus replicates itself. The twin copies of the
chromosomes stay close to each other at first and are
called “sister chromatids”. The point of attachment
of two sister chromatids is called a “centromere”.
Meiosis I
Prophase I: Over 90% of the time cells spend in
meiosis occurs in Prophase I. The chromosomes,
sister chromatids still linked at centromeres, start to
condense and, as prophase continues, the
chromosomes thicken until they are clearly visible
with a light microscope. Homologous chromosomes
come close together to form complexes of four
chromatids, called “tetrads”. The close association of
homologous genes allows “crossing-over” to occur
between homologous chromosomes.
Metaphase I: Tetrads line up so that the
centromeres of homologous chromosomes point
toward opposite poles.
During a crossover event, segments of adjacent “nonsister” chromatids can exchange by breaking and
reattaching to the other chromatid.
As the spindle fibers form, the nuclear envelope
dissolves and the tetrads begin moving to a spot
midway between the two poles of the spindle fibers.
MeiosisSimulation.BWG.doc 02/02/12
Anaphase I: The spindle fibers separate the tetrads
by pulling homologous chromosomes toward
opposite poles. Sister chromatids remain attached at
the centromeres.
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Telophase I: The chromosomes continue to move to
the poles. Two daughter cells are formed when
cytokinesis (e.g. division of the cytoplasm) occurs.
Interphase II: The period of interphase between
Meiosis I and Meiosis II is usually very short. There
is no further DNA replication. All of the materials
needed for a second nuclear division is synthesized.
In some organisms the nuclear envelope reforms and
the chromosomes disperse.
Metaphase II: Sister chromatids line up with the
centromeres between them.
Anaphase II: The centromeres that join two sister
chromatids break apart and sister chromatids move
toward opposite poles. Because of the crossing-over
that occurred during Prophase I, these “sister”
chromatids are genetically different.
Meiosis II
Prophase II: Unlike Prophase I, this stage is brief.
Depending on what happened during the Interphase
stage, chromosomes may recondense and become
visible and the nuclear envelope may dissolve. In
each new cell the centrioles move to the poles and
new spindle fibers form. The new spindle forms at a
right angle to the spindle in Meiosis I. The
chromosomes begin moving toward the center.
Telophase II: Nuclei start to form around
chromatids at opposite poles of the cell. Cytokinesis
occurs. The results is four daughter cells, each with a
haploid number of chromosomes.
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Activity
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What to do…
Safety: This lab activity uses small parts which may
represent a choking hazard. Be sure that you follow
your teacher’s directions and take precautions when
working with these parts.
Simulating Meiosis and Fertilization
Modeling Meiosis I
What you need
Materials needed per team:
16
Centrioles
16
Centromeres, magnetic
Colored pencils (blue, green, red and yellow)
34
Pop beads, blue
34
Pop beads, green
34
Pop beads, red
34
Pop beads, yellow
Step 1
……………………………………………………….
Form a team of 4 to 6 students as directed by your
teacher. Divide each team into two groups, “A” and
“B”. Divide the pop beads between the two groups
so that each group has beads of two different colors.
Each color represents a chromosome from a different
parent. Each group will simulate the stages of
meiosis to make four haploid cells from one diploid
cell. One group will be making haploid cells for
eggs, the other for sperm. At the end of meiosis, the
two groups will reunite to simulate the fertilization of
one egg by one sperm.
Step 2
……………………………………………………….
Interphase I
Each group will build two homologous pairs of
chromosomes, a long pair and a short pair. Students
in Group A will assemble a long homologous pair of
chromosomes using 10 blue pop beads for one
member of the chromosome pair and 10 red pop
beads for the other member of the pair. Place the
centromere at any position in the chromosome but
note that it must be in the same position on
homologous chromosomes. Then assemble the
shorter chromosome pair, using the 7 pop beads of
the same colored pop beads for each. Students in
Group B will assemble a similar set of a short and a
long homologous pairs of chromosomes using the
green and yellow pop beads. To begin the simulation
of meiosis, pile your chromosomes on the Interphase
I spot on the meiosis worksheet, along with a pair of
centrioles as they would appear in a living cell.
MeiosisSimulation.BWG.doc 02/02/12
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Step 3
………………………………………
Draw a diagram to show what your
simulated cell nucleus looks like
before meiosis begins. Use colored pencils to color the two
pairs of homologous
chromosomes.
Step 4
……………………………………………………….
To simulate DNA replication, make copies of your
chromosome pairs. Although there is only one
centromere between two sister chromatids in an
actual cell, you will need to use one magnetic
centromere for each chromatid.
Step 6
……………………………………………………….
Metaphase I
Step 5
……………………………………………………….
Prophase I
Step 7
……………………………………………………….
Anaphase I
Separate the two centriole pairs and move them to
opposite ends of the Prophase I spot on the worksheet. Move each homologous chromosome so that it
pairs with its partner. You should have one tetrad of
long chromosomes and one of short chromosomes.
Simulate Anaphase I by separating homologous pairs
and moving one homologue toward each pole. Sister
chromatids should still be connected through the
centromeres.
Simulate crossing-over by removing and exchanging
identical segments of any two non-sister chromatids
in a tetrad. The crossover site is called a “chiasma”.
Move your tetrads to a region midway between the
two centriole pairs. This is called the “equator”.
Step 8
……………………………………………………….
Telophase I
MeiosisSimulation.BWG.doc 02/02/12
Align the tetrads at the equator so that the
centromeres of homologous pairs face toward
opposite poles.
Place the chromosomes at the poles. You should
have one long and one short chromosome at each
pole, representing a homologue from each pair.
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Step 9
………………………………………………………………………………………………………………………
Draw a diagram to show what your simulated cells look like at the end of Meiosis I.
Questions
1.
Are the two daughter cells diploid or haploid? Explain.
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2.
Use the drawings you have made to compare the original cell to the two daughter cells at the end of
Meiosis I. How are the daughter cells different from the original cell?
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Modeling Meiosis II
Step 10
……………………………………………………….
Interphase II
To simulate Interphase II, move the chromosomes
formed at the end of Meiosis I to the two spots
indicated on the worksheet. Duplicate the centriole
pairs.
Step 11
……………………………………………………….
Prophase II
Separate the centrioles and set up the axes of the two
new spindles. Pile the chromosomes in the center of
each spindle. Move the chromosomes to the equator
of their respective spindles.
Step 12
……………………………………………………….
Metaphase II
Arrange the chromosomes with the centromeres lined
up along the equator to simulate Metaphase II. One
chromatid should be facing one pole while its sister
chromatid faces the opposite pole. Pull the two
magnets of each chromatic pair apart.
Step 13
……………………………………………………….
Anaphase II
Separate the sister chromatids and move them to
opposite poles.
Step 14
……………………………………………………….
Telophase II
Pile the chromosomes at the poles to simulate
Telophase II.
Step 15
………………………………………………………………………………………………………………………
Draw a diagram that shows what your simulated cells look like at the end of Meiosis II.
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Conclusions
1. Are the four daughter cells diploid or haploid?
Explain.
________________________________________
________________________________________
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2.
Use the drawings you have made to compare
the four daughter cells at the end of Meiosis II
and the two daughter cells at the end of Meiosis I
and to the original cell.
________________________________________
________________________________________
________________________________________
3.
Compare the four daughter cells with each
other. How are they similar? How are they
different?
________________________________________
Modeling Fertilization
Step 16
……………………………………………………….
Reunite with your group in your team. Each group
should now have four haploid cells. That is, each
will have four cells with one set of chromosomes
each. Choose one cell from one group to represent
the egg and one cell from the other group to represent
the sperm. To simulate the pooling of chromosomes
after the fusion of the two cells, bring together the
chromosomes from the egg and the sperm on the
“Zygote” spot on the “Modeling Fertilization”
worksheet.
Step 17
……………………………………………………….
Draw a diagram to show what your simulated cell
nucleus looks like after pooling the chromosomes
from sperm and egg nuclei. Use colored pencils to
color the two pairs of homologous chromosomes.
________________________________________
________________________________________
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Questions
1. After fertilization, is the cell diploid or haploid? Explain.
_______________________________________________________________________________________
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2.
Use the drawings you have made to compare the cell after fertilization to the original cell before
meiosis. How are they different, and how are they similar?
_______________________________________________________________________________________
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3.
If the chromosome number was not reduced during meiosis, what would happen during fertilization?
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4.
Describe the different ways genes are rearranged during meiosis.
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Going Further
What happens if something goes wrong during one of the steps in meiosis and the chromosomes do not separate
properly? Do a little reading about Kleinfelter’s syndrome and Turner’s syndrome, two examples of what
happens when the sex chromosomes do not separate properly during meiosis.
Use a pop bead of a different color to mark a gene for a particular trait. What happens to the gene for that trait
as meiosis proceeds?
Learn & Read More About It
The Cartoon Guide to Genetics, Larry Gonick and Mark Wheelis, HarperPerennial, 1991.
Life Itself: Exploring the Realm of the Living Cell, Boyce Rensberger, Oxford University Press, 1996.
Molecular Biology of the Cell, Bruce Alberts, et al., 3rd Edition, Garland, 1994.
Neat Websites
Cell Division: Meiosis and Sexual Reproduction. Overview with diagrams from the “Online Biology Book”:
http://gened.emc.maricopy.edu/bio/bio181/BIOBK/BioBookmeiosis.html
Virtual Meiosis Page: http://www.biology.uc.edu/vgenetic/meiosis/
Meiosis--Movies: http://www.mcgill.ca:80/nrs/meiosis.htm
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