Mitosis & Meiosis Exercise
Part I: Mitosis
In this exercise, we will be following the fate of two different chromosomes (#14 & #8) in a
diploid cell as they undergo mitosis. In diploid organisms, chromosomes occur in matched pairs called
homologous chromosomes. These are identical in size, shape, location of their centromeres, and
types of genes present. One member of each homologous pair (the homolog) is contributed by the
“male” parent and one is contributed by the “female” parent during the process of sexual reproduction.
When the chromosomes replicate, each homologous chromosome becomes two identical sister
chromatids. In this exercise, the yellow beads will represent chromosomes from the “male” parent
and the red beads will represent chromosomes from the “female” parent.
Each group will need:
1 dry erase pad
Marking pen
44 red beads
44 yellow beads
8 centromeres (white tubes)
2 pennies (centrosomes)
Make the following chromosomes (see Figure 1 for example):
Chromosome #14:
2 red chromosomes that are 14 beads long, with the centromere placed in the middle.
2 yellow chromosomes that are 14 beads long, with the centromere placed in the middle.
Chromosome #8:
2 red chromosomes that are 8 beads long, with the centromere placed in the middle.
2 yellow chromosomes that are 8 beads long, with the centromere placed in the middle.
Step through the process of mitosis, as described below. As one team member works their way
through the exercise, the other team member should be making a labeled diagram of each stage. At the
end, reverse the roles so each team member has a chance to walk through the steps.
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

Begin by drawing a large circle representing a cell on the pad. In the cell draw a nucleus large
enough to contain the chromosomes you have made.
Place the homologues for chromosome #14 (one red and one yellow) separately in the nucleus.
Place the homologues for chromosome #8 (one red and one yellow) separately in the nucleus.
G2 Interphase:
 Chromosomes duplicated - For each homologue, attach its copy (sister chromatid) (e.g., red with
14 beads to red with 14 beads) at the centromere.
Prophase:
 Chromosomes condense and become visible
 Centrosomes start to move, one towards each pole of cell. Centrosomes are sites of microtubule
formation. – Move pennies to represent centrosomes (one heading north, one south).
 The mitotic spindle (microtubules) start to form, radiating from the centrosomes – Draw lines from
the centrosomes that are heading towards the chromosomes.
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Mitosis & Meiosis Exercise
Prometaphase:
 Nuclear envelope breaks down – Erase it from the pad.
 Mitotic spindle starts to attach to chromosomes at the centromere
 - For each chromosome, the microtubules from the “northern” centrosome will attach to one sister
chromatid at the kinetochore (special attachment protein at centromere), and the microtubules from
the “southern” centrosome will attach to the other sister chromatid. Draw lines representing this.
 Non-kinetochore microtubules interact with others from opposite pole
 The chromosomes will begin moving towards the midline (equator) of the cell (called the
metaphase plate).
Metaphase:
 Centrosomes have reached opposite poles
 Chromosomes will be lined up individually along the metaphase plate – Move the chromosomes
until they form a single file line along the midline of the cell.
 Each sister chromatid is attached to a kinetochore microtubule – Erase and redraw the microtubule
lines reaching from the centrosomes to the centromere of each sister chromatid. Again, the
“northern” centrosome should have a microtubule attached to the sister chromatid closest to it, and
the “southern” centrosome should have a microtubule attached to the sister chromatid closest to it.
 Other non-kinetochore microtubules meet with each other from opposite ends of the cell
Anaphase:
 Sister chromatids of each chromosome separate and start to move towards “north” and “south”
poles of cell – Separate the 2 sister chromosomes by pulling the centromeres apart from each other.
 Cell elongates as microtubules push poles of cell further apart.
 End of Anaphase -Each sister chromatid (now a separate chromosome) is now at separate ends of
cells – Move them to the poles of the cell.
Telophase:
 Nuclear envelope reforms - Draw a nuclear envelope around the chromosomes at each pole.
 Mitotic spindle goes away – Erase it.
Cytokinesis:
 A division occurs along the midline of the cell separating it into two cells – Draw a line separating
the two cells.
Using the drawings your teammate made, compare the cell at the end of Interphase with the cells you
end up with at the end of Cytokinesis.
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Mitosis & Meiosis Exercise
Part II: Meiosis
Meiosis consists of two nuclear divisions (meiosis I and meiosis II) and results in the
production of four daughter nuclei, each of which contains only half the number of chromosomes (and
half the amount of DNA) characteristic of the parental cells.
During meiotic reduction of the chromosome number to half, however, chromosomes are not
just divided into two sets at random. In diploid organisms, chromosomes occur in matched pairs called
homologous chromosomes. Meiosis provides as precise a mechanism as possible for separating
these homologous chromosomes so that daughter cells carry one member, or homologue, of each
chromosomal pair.
Meiosis also serves as a mechanism for increasing genetic diversity. One way that genetic
diversity is increased is by crossing over. This is when two homologous chromosomes exchange
corresponding segments.
In this exercise, we will be following the fate of two different chromosomes (#14 & #8) in a
diploid cell as they go through the process of meiosis. Use the same chromosomes you put together
previously. Step through the process of meiosis, as described below. As one team member works
their way through the exercise, the other team member should be making a labeled diagram of
each stage. At the end, reverse the roles so each team member has a chance to walk through the steps.



Begin by drawing a large circle representing a cell on the pad. In the cell draw a nucleus large
enough to contain the chromosomes you have made.
Place the homologues for chromosome #14 (one red and one yellow) separately in the nucleus.
Place the homologues for chromosome #8 (one red and one yellow) separately in the nucleus.
G2 of Interphase:
 Chromosomes duplicated - For each homologue, attach its copy (sister chromatid) (e.g., red with
14 beads to red with 14 beads) at the centromere.
Prophase 1:
 Chromosomes condense and become visible.
 Homologous chromosomes stuck together in pairs (4 sister chromatids - called a tetrad) – Attach
duplicated chromosome from mother (red) to duplicated chromosome from father (yellow) at
centromeres.
 Crossing over occurs – For chromosome #14, remove a segment of red beads from one
homologous chromosome and exchange it with the same number of yellow beads from the other
homologous chromosome. Do the same with chromosome #8.
 Nuclear envelope breaks down – Erase it from the pad.
 Centrosomes start to move towards poles of cells – Move pennies to represent centrosomes (one
heading north, one south).
 Mitotic spindle forms & attaches to chromosomes at the centromere - For each tetrad, the
microtubules from the “northern” centrosome will attach to one of the duplicated chromosomes,
and the microtubules from the “southern” centrosome will attach to the other duplicated
chromosome. Draw lines representing this.
 The tetrads begin moving towards the metaphase plate.
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Mitosis & Meiosis Exercise
Metaphase 1:
 Tetrads will be lined up along the metaphase plate – Move the tetrads until they form a line along
the midline of the cell.
 Each duplicated pair of homologous chromosome will be attached to a microtubule – Erase and
redraw the microtubule lines reaching from the centrosomes to the centromere of each duplicated
chromosome. Again, the “northern” centrosome should have a microtubule attached to the
duplicated chromosome closest to it, and the “southern” centrosome should have a microtubule
attached to the duplicated chromosome closest to it.
Anaphase 1:
 Pairs of duplicated chromosomes separate and start to move towards “north” and “south” poles of
cell – Separate the tetrad by pulling the centromeres of the pairs of homologous chromosomes
apart from each other.
 Cell elongates as microtubules push poles of cell further apart.
Telophase 1:
 Duplicated homologous chromosomes now at separate ends of cells – Move them to the poles of
the cell.
 Nuclear envelope reforms - Draw a nuclear envelope around the chromosomes at each pole.
 Mitotic spindle goes away – Erase it.
Cytokinesis 1:
 A division occurs along the midline of the cell separating it into two cells – Draw a line separating
the two cells.
Using the drawings your teammate made, compare the cell at the end of Interphase 1 with the cells you
end up with at the end of Cytokinesis 1.
Starting with one of the cells you end up with after the first round of meiosis, continue with the second
round of meiosis.
Prophase 2:
 Centrosomes start to move towards poles of cells – Move pennies to represent centrosomes (one
heading north, one south).
 Nuclear envelope breaks down – Erase it from the pad.
 Mitotic spindle starts to form and to attach to chromosomes at the centromere - For each
chromosome, the microtubules from the “northern” centrosome will attach to one sister chromatid,
and the microtubules from the “southern” centrosome will attach to the other sister chromatid.
Draw lines representing this.
 The chromosomes will begin moving towards the metaphase plate.
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Mitosis & Meiosis Exercise
Metaphase 2:
 Chromosomes will be lined up individually along the metaphase plate – Move the chromosomes
until they form a single file line along the midline of the cell.
 Each sister chromatid will be attached to a microtubule – Erase and redraw the microtubule lines
reaching from the centrosomes to the centromere of each sister chromatid.
Anaphase 2:
 Sister chromatids of each chromosome separate and start to move towards “north” and “south”
poles of cell – Separate the 2 sister chromosomes by pulling the centromeres apart from each other.
 Cell elongates as microtubules push poles of cell further apart.
Telophase 2:
 Each sister chromatid (now separate chromosomes) is now at separate ends of cells – Move them to
the poles of the cell.
 Nuclear envelope reforms - Draw a nuclear envelope around the chromosomes at each pole.
 Mitotic spindle goes away – Erase it.
Cytokinesis 2:
 A division occurs along the midline of the cell separating it into two cells – Draw a line separating
the two cells.
Using the drawings your teammate made, compare the cell at the end of Interphase 1 with the cells you
end up with at the end of Cytokinesis 2.
On the drawings you have made, make note of the stages where mitosis and meiosis differ. Be as
specific as possible.
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