Mitosis and Meiosis Lab
Mitosis and meiosis are both forms of cell division and share similar details and
terminology. This laboratory combines the study of the two processes in order to better
understand the similarities and differences between the two.
All multicellular organisms began life as a single fertilized egg cell (zygote). In order to
grow and develop, that zygote has to divide and subsequent cell divisions ultimately
arrive at an organism comprised of countless cells, many specialized for specific
functions but all identical genetically to the original zygote While the overall division of
a cell membrane and cytoplasm in half is termed cytokinesis, the more complicated
replication and division necessary for identical daughter cells is mitosis, the division of
the nucleus which involves the separation of the chromosomes. While most attention is
usually spent on the mitotic phase, it is only one part of the cell cycle, the life of a cell
from its formation to when it divides itself. The part of the cycle other than mitosis is
called Interphase and it is further subdivided into the Gap 1 phase (G1), Synthesis
phase (S), and Gap 2 phase (G2).
During G1 phase, the cell generally proceeds with its normal cell functions including
growth and synthesis of cellular products other than DNA. For example, if the cell in
question is an islet cell of the pancreas, it will be busy producing and exporting the
protein insulin which the body uses to regulate sugar levels in the bloodstream. Some
cells will exit the cell cycle at the end of the G1 phase and enter the G0. phase. A cell in
this phase will not proceed with cell division. Some adult cells such as the cells in the
central nervous system stay permanently in the G0 phase while others will remain there
indefinitely until cell division is needed for repair. If the cell passes from the the G1
stage into the S phase, it has committed to replicate and divide. During the S phase,
the DNA in the chromosomes is replicated so that at the end of S phase, each
chromosome consists of identical pairs of chromosomal DNA strands called sister
chromatids attached by a structure called a centromere. During G2 phase, the cell
continues to manufacture materials that will be needed for the upcoming mitotic phase.
Mitosis separates the genetic material that was duplicated during the S phase of
interphase into two identical sets of chromosomes and also reforms the nuclear
membrane so that the resulting daughter cells have identical nuclei when cytokinesis is
complete. Mitosis is typically subdivided into 5 stages (Prophase, Prometaphase,
Metaphase, Anaphase and Telophase), but it is important to remember these stages
are only to make it easier to understand what is occurring. The actual process of mitosis
is a fluid, continuous sequence with each “stage” flowing into the next without any
At the end of mitosis, the cell can then undergo cytokinesis. This process is slightly
different depending on if the cell has a cell wall such as a plant cell or is an animal cell
without a wall. In animal cells, a cleavage furrow begins on the periphery of the cell
membrane, pinches inward and eventually divides the cytoplasm into two cells. The
protein microfilaments are instrumental in contracting and pinching the two daughter
cells apart. In cells with a cell wall, cytokinsesis involves the formation of a partition
called a cell plate which forms in the middle of the cell and grows to the cell’s edges to
divide the daughter cells. When cytokinesis has been completed, the result is two
daughter cells that have identical nuclei with the same DNA.
The second form of cell division is meiosis which is the process of nuclear division that
reduces the number of chromosomes in half. For many organisms, meiosis is the
process that produces gametes, the sex cells (sperm or egg). In organisms that
reproduce sexually, chromosomes are typically diploid (2n), that is they occur as pairs
in the nucleus of somatic cells (any cells other than the gametes). The two
chromosomes of a pair are called homologous chromosomes (homologues) and
each homologue of a pair has the same sites or loci for the same genes as its partner.
Meiosis reduces the number of chromosomes to the haploid (n) state. This reduction is
very important so that when two gametes fuse during fertilization, the diploid number is
restored in the new individual. Additionally, meiosis can shuffle the genetic material so
that each resulting cell carries a new and unique set of genes. While many of the
stages of meiosis are similar to mitosis, it is important to remember the differences as
well. Overall, meiosis involves two divisions of the cells (Meiosis I and Meiosis II)
while mitosis involves only one. More importantly, there is no synthesis of DNA
between the two divisions in meiosis creating the desired haploid state at the end of
meiosis. Remember that mitosis creates two identical diploid daughter cells but meiosis
will create four haploid daughter cells, each unique in their specific DNA makeup from
each other and their parental cell
Mitosis and Meiosis Worksheet
Assume you are viewing somatic fruit fly cells undergoing mitosis under a microscope.
Using your textbook as a guide, draw each stage of mitosis in the circles below
(representing cell membranes). Assume these parental cells have 4 chromosomes
(remember DNA is duplicated in the S phase). Your diagrams should include the
following labeled terms and structures:
nuclear membrane fragments
Telophase Cytokinesis (animal cell)
Now assume your above cells were onion cells, not fruit fly cells. Draw below the
difference in cytokinesis you would expect with a plant cell, labeling all important
Obtain: pre-made slides of cells undergoing mitosis, light microscope
Procedure: View the slides under your microscope and attempt to identify cells in the
various stages of mitosis.
Fill in the following diagram of meiosis, following the chromosomes (chromatids), in a
cell with 2n=4. Number each sister chromatid 1-8 so that you can follow them
through the divisions. Do not worry about the individual stages of meiosis. Note that
there are 2 pairs of homologous chromosomes, with each homologue consisting of a
pair of sister chromatids.
Parental cell at G2
End of Meiosis I after
End of Meiosis II
Modeling of Crossing Over: This exercise demonstrates the occurrence of crossing
over (exchange of genetic material between non-sister chromatids of homologous
chromosomes) that occurs in Prophase I of Meiosis I.
Obtain: 40 beads of one color; 40 beads of different color; 4 pieces of pipe cleaners
long enough to hold 20 beads each; 2 shorter pieces of pipe cleaners
a.) Using the longer pieces of pipe cleaners, make two sister chromatids of 20 same
colored beads each. Hold them together with the shorter piece of pipe cleaner at the
center, representing the centromere.
b.) Make a homologue (with sister chromatids) of the pair of sister chromatids from a.)
by using the other color of beads. Lay them next to the first pair forming a tetrad.
c.) Cross equal sections of non-sister chromatids (i.e. chromatids of different colors)
and exchange 3 beads each.
Modeling of Independent Assortment. This exercise demonstrates Mendel’s Law of
Independent Assortment which details the random arrangement of homologous
chromosomes during Metaphase I.
Obtain: pipe cleaners--2 each of two different colors and three sizes (small, medium,
large) for a total of 12 pieces
a.) Twist the two pipe cleaners of each size and same color together, forming sister
chromatids. You should have 6 pairs of sister chromatids representing 3 pairs of
homologous chromosomes (with each member of the homologous pair the same size
as its homologue but each a different color).
Designate which color originates from the father: _______________________
Designate which color originates from the mother: _______________________
b.) Form tetrads of the homologues and line them up at an imaginary Metaphase I plate
in any arrangement you wish.
c.) Simulate Anaphase I by separating the homologues, moving them towards opposite
d.) Finish Meiosis II by forming four daughter cells by separating sister chromatids.
e.) Describe the genetic makeup of your resulting daughter cells in terms of their
paternal or maternal origin based on color.
f.) Repeat procedures a-d but change the random pattern of homologues lining up at
Metaphase I from what you did the first time.
g.) Describe the genetic makeup of your resulting daughter cells for this round of
meiosis. How does it differ from what you described in the earlier division?