Download Meiosis Modeling Activity

Biology I Lab Activity – Simulating Meiosis with “Pop Beads”
Introduction: Meiosis involves two cell divisions (one after the other) that produce four
haploid cells from one diploid parent cell. Meiosis I, the first cell division, is called the
reduction division because the number of chromosomes in a cell is divided in half (i.e. diploid
 haploid). Meiosis II, the second cell division, separates the sister chromatids of each
duplicated chromosome in the two cells that were produced during Meiosis I.
Mitosis produces new cells that are identical (Is this a true statement?) to the original parent
cell. Meiosis, on the other hand, produces cells that are genetically distinct from the original
parent cell. As you work through the simulation, you should discover two different ways that the genetic information
stored on chromosomes can be changed during meiosis.
Instructions: In this activity you will use chromosome simulation kits (“Pop Beads”) to investigate the process of
meiosis. Your kit should include two strands of beads of one color and two strands of beads of a second color. A
homologous pair of chromosomes is represented by one strand of each color, with one member of each pair
coming from one parent.
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Meiosis I – Produces haploid cells from a diploid parent cell.
Step 1 – Interphase
Place one strand of each color near the center of your work area. Before meiosis can begin, DNA is copied
during interphase, and each chromosome, originally composed of one strand will be copied so that it is now made of
two separate strands connected by a centromere. You should note that each DNA strand has its’ own centromere
and the connection between DNA molecules occurs at this point.
Simulate DNA replication by bringing the magnetic centromere region of one strand in contact with the
centromere region of the other strand (of the same color). Do the same with it homologous chromosome partner.
Step 2- Prophase I
Homologous chromosomes come together and sister chromatids wrap
around each other to form tetrads. Tetrads are composed of four sister
chromatids from two homologous chromosomes. Tetrads allow for crossing
over, the exchange of genetic material between two non-sister chromatids.
Use your models to simulate a crossover. Pop off one or more beads at
the end of one sister chromatid and do the same with another sister chromatid
on the homologous chromosome. Reconnect the beads. Note how crossing
Before
A!er
over creates genetic variation. The chromosomes now carry different
information than they had at the beginning of meiosis. Draw a picture of your chromosomes before and after
crossing over in the box. Use two different colors to represent maternal and paternal chromosomes.
Step 3 – Metaphase I
The tetrads line up in the center of the cell. Position the chromosomes
in the middle of the cell. Draw a picture of the chromosomes in your imaginary
cell in the box to the right. Include a sketch of the spindle that aids in the
positioning of the chromosomes in the middle of the cell.
Question: Is there more than way that the chromosomes can line up in the
middle of the cell during metaphase I? Does this make a difference in later stages of meiosis?
Step 4- Anaphase I
During anaphase I, homologous chromosomes separate and are “pulled” to opposite sides of the cell by the
spindle. Anaphase I begins the process of reducing the chromosome number by half (i.e. diploid  haploid).
Step 5 – Telophase I and Cytokinesis
Place each chromosome at opposite sides of the cell. Recall that during telophase of mitosis, the animal cell
membrane pinches in and divides the cytoplasm into two new cells. The same sort of process takes place during
telophase I of meiosis I.
Notice that each chromosome within the two new cells still consists of two sister chromatids connected at the
centromere. At the end of telophase I, each new cell contains a haploid number of chromosomes compared to the
original parent cell.
Meiosis II – Produces four haploid daughter cells from the two haploid cells produced during
meiosis I. Meiosis II is almost identical to mitosis.
Step 6 – Prophase II
Each of the cells generated in Interphase I progress into Interphase II. However, no DNA replication occurs
between meiosis I and meiosis II. The meiotic spindle reforms between centrioles positioned at opposite ends of the
cell.
Step 7 – Metaphase II
Position the chromosomes so that they are centered in the middle of each cell that was produced during
meiosis I. Note the difference in chromosomal alignment in Metaphase II compared to Metaphase I.
Step 8 – Anaphase II
The centromeres that hold the sister chromatids of each chromosome
together separate. The spindle pulls sister chromatids to opposite sides of the
cell. Each separated chromosome is now referred to as a single (daughter)
chromosome. Draw a picture of the separated sister chromatids in each cell
in the box to the right.
Step 9 – Telophase II and Cytokinesis
Place the chromosomes at opposite ends of each dividing cell. As
before, the cell membrane pinches in and separates the cytoplasm in each cell.
The end result is the production of four haploid daughter cells from the two
cells produced during meiosis I. Draw a picture of the four cells (and the
chromosomes within each cell) that are produced at the end of meiosis in the
box to the right. You are encouraged to use different colors to differentiate
between the chromosomes in each of the daughter cells.
Analysis Questions
1. List 3 differences between mitosis and meiosis. You may use your textbook and/or the class notes if you need
help.
2. Why is meiosis important for sexual reproduction?
3. Can you think of two ways that meiosis could produce gametes that contain genetic material that is different from
the parent cell?