Biology
140 –
Human
Biology
Lab
Notebook –
Cell
Division
Laura Ambrose
Luther College © 2012
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Contents
Cell Division ................................................................................................................................................. 32
Introduction ............................................................................................................................................ 32
Learning Goals..................................................................................................................................... 33
Learning Objectives ............................................................................................................................. 33
Checklist of topics covered and in-lab activities to complete ............................................................ 33
Background ............................................................................................................................................. 34
Chromosomes ..................................................................................................................................... 34
Replication .......................................................................................................................................... 35
The Cell Cycle ...................................................................................................................................... 35
Scenarios of when mitosis occurs in the human body ....................................................................... 36
Scenarios of when meiosis occurs in the human body ....................................................................... 37
Spermatogenesis ................................................................................................................................. 38
Spermatogenesis ................................................................................................................................. 39
Oogenesis ............................................................................................................................................ 40
The complete picture .......................................................................................................................... 41
Readings .................................................................................................................................................. 42
Pre-lab Questions.................................................................................................................................... 42
Lab activities and worksheets ................................................................................................................. 42
Replication .......................................................................................................................................... 42
Mitosis in the human body: Infection! White blood cells to the rescue! ........................................... 45
The mitosis activity ............................................................................................................................. 47
Meiosis: And baby makes…92? ........................................................................................................... 48
The meiosis activity ............................................................................................................................. 48
Lab assessments...................................................................................................................................... 50
In lab.................................................................................................................................................... 50
Homework........................................................................................................................................... 50
Study guide ............................................................................................................................................. 50
Bibliography ............................................................................................................................................ 51
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Cell Division
Introduction
Growth occurs when cells increase in number. Cell number grows when a cell, the parent cell, moves
through a series of steps and changes to get ready to divide in half, creating two daughter cells. The
steps, or changes the cells go through, is referred to as the cell cycle. You can think of the cell cycle as
the life cycle of the cell, from when the cell forms to when the cell divides.
In the human body, there are two types of cell division that occur. One type, mitosis, is the cell division
used by body cells for growth of the body and repair of tissues. For example, when a person breaks their
arm, the bone tissue responds by producing more bone cells to heal the break. The new bone cells are
produced from existing bone cells by the process of mitosis. The other type of cell division, meiosis, is
used very specifically to produce cells that will be used for sexual reproduction. In this type of division,
the parent cell divides in half as in mitosis, but the two daughter cells also divide in half, producing 4
daughter cells for each parent cell that started the process. The biggest difference between mitosis and
meiosis, however, is inside the cell. In meiosis, the daughter cells have half the amount of DNA that was
found in the parent cell.
Cell division is a controlled occurrence in that cells only divide when they receive the signal to divide.
The signal comes from a variety of sources, such as when you cut your hand and your immune system
sends out the signal for extra skin cells to repair the wound. Another example is when a secondary
oocyte contacts a mature sperm cell to move through the second stage of meiosis in order to produce
an ovum that can fuse with the sperm.
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There are some instances where the cell division process fails. In the case of a skin tag, the skin cells fail
to recognize when there are enough skin cells and more cells than necessary are produced, creating a
flap of skin. A more serious example of when the control mechanism for cell division fails is the case of
cancer. In cancer, the cells are altered at a genetic level and no longer respond to the control
mechanisms that regulate when a cell divides.
All cells, from bacteria to human body cells, follow the same basic process for division:
1. Copy the DNA and necessary cell components, and
2. Divide the parent cell in half.
This lab will look at the steps that human body cells follow as they divide by mitosis or meiosis.
Learning Goals
 To introduce the concept of the chromosome
 To introduce the process of DNA replication
 To introduce the process of mitosis as the mechanism used for growth and repair
 To introduce the process of meiosis as the mechanism that produces cells used for reproduction
Learning Objectives
- After a demonstration and discussion, the student will understand how the DNA within human
body cells is organized into chromosomes
- After viewing a video and reviewing the process, the student will understand how chromosomes
are copied for cell division
- After a review of the process of mitosis, the student will be able to describe the process and
provide appropriate examples of when mitosis occurs in the human body
- After a review of the process of meiosis, the student will be able to describe the process
- After reviewing posters, watching a video, and using other resources, the student will be able to
describe the processes of oogenesis and spermatogenesis
- After all of the lab exercises have been completed, the student will be able to describe the life
cycle of a human from conception to reproduction, in terms of when mitosis and meiosis occur
and how males and females combine genetic material to produce the next generation
Checklist of topics covered and in-lab activities to complete
o View the DNA ball and stick model to get an idea of the 3-D structure of the double helix
o Replication practice
o View the video on DNA replication (HHMI)
o View the video on mitosis (Cells Alive!)
o View the posters and models of mitosis
o View the microscope slides of mitosis and draw the four stages
o Do the mitosis simulation activity (Triffle)
o View the video on meiosis (Cells Alive!)
o View the posters and models of meiosis
o Do the meiosis simulation activity (Piffle)
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Background
Mark and Angela have decided that they would like to have a baby. Mark’s body busily makes sperm on
a daily basis when cells in his testes divide first by mitosis to make a lot of primary spermatocytes and
then by meiosis to change the primary spermatocytes into mature sperm. Angela’s body did things a
little bit differently in that when she was still a fetus, cells in her ovaries divided by mitosis to produce a
lot of primary oocytes which then went through the first half of meiosis to produce secondary oocytes.
These secondary oocytes then remained in Angela’s ovaries until her body started to go through
puberty, releasing one at a time from an ovary on some sort of schedule. If the released secondary
oocyte did not connect with a sperm, as what happened so far with Mark and Angela, it was released
from the body during menstruation. If, what Mark and Angela were hoping would happen now, the
secondary oocyte connects with a sperm, the secondary oocyte will quickly finish the second half of
meiosis to produce an ovum to fuse with the sperm to create the zygote, the first cell of the next
generation.
-
-
Mitosis is the cell division that produces more of the same kind of cell. Meiosis is the cell division
that produces gametes, cells used for sexual reproduction. The steps of mitosis are similar to
the steps of meiosis, with some key differences:
The daughter cells produced by mitosis are identical to each other and the parent cell
The daughter cells produced by meiosis contain half the genetic information as the parent cells
and are not identical to each other
There are two daughter cells produced from each parent cell after mitosis
There are four daughter cells produced from each parent cell after meiosis
Chromosomes
If you were to take a human body cell, say a cell from the lining of the stomach, and empty the contents
on the table, then sort through everything until you found the nucleus and open it up and dump the
nuclear contents on the table, you would notice that the DNA occurs as 46 distinct pieces, rather than
one super long piece. Each piece of DNA is called a chromosome, so there are 46 chromosomes in
human body cells.
As you look more closely, you would notice that you could start to sort the chromosomes based on
some physical characteristics:
- Length of the chromosome
- Banding pattern (stripes of dark and light, as seen under the light microscope)
- Centromere location (a specific spot on the chromosome where two copies can stick together)
And, if you put on your DNA reading glasses, you would notice one genetic characteristic:
-
-
Genes for the same traits at the same place along the chromosome (for example, if one
chromosome has a gene for eye colour at a particular spot on the chromosome, there would be
another chromosome with a gene for eye colour at the same place)
Note: The genes are for the same traits, but they are not necessarily the same. For example, in
one chromosome pair you could have genes for eye colour with one gene being instructions for
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brown eyes and one gene being instructions for blue eyes. These different types of genes are
called alleles. So, in this example, the chromosome pair would have a brown eye allele and a
blue eye allele.
Based on these 4 characteristics, you would notice that chromosomes are organized into pairs. The 46
chromosomes in the human body cells exist as 23 pairs of chromosomes. The pairs are referred to as
homologous chromosomes or homologous chromosome pairs.
Replication
In order for a parent cell to divide to produce daughter cells, many cell components, including DNA and
cell organelles, have to be copied so there is twice as much of them as what is needed in a normally
functioning cell. With regards to chromosomes, the copying process is called replication.
Within the nucleus there are large protein molecules called enzymes that can read the chromosomes
and then make a copy of them to produce two identical copies. The copies are called chromatids, or
sister chromatids. In biology the suffix –tid is added to word to refer to a structure or cell that is
immature. Therefore the chromatids are not functioning chromosomes, but immature chromosomes.
The chromatids are held together after they are copied at a specific place called the centromere, and
they are held together until the cell division process pulls them apart.
Replication begins when there is a signal that the cell is to divide. Inside the nucleus the enzymes attach
themselves to one end of the chromosome and start reading it, making a copy as it goes along. After the
enzyme reaches the other end of the chromosome, there are two chromatids, held together at the
centromere. At this point the cell is fully committed to dividing as the chromosomes are not able to
function, which means the cell cannot function.
If you were to count up all of the unique chromosomes in the cell, you would find there are still only 46
unique chromosomes, however each of those chromosomes would be copied.
Prior to your lab period, view the animations of replication:
http://www.hhmi.org/biointeractive/dna/DNAi_replication_vo1.html
http://www.cellsalive.com/cell_cycle.htm (look for replication in S phase)
The Cell Cycle
The cell cycle is the stages a cell moves through starting when it is formed and ending when it divides.
Researchers have broken down the cell cycle into phases based on the activities that the cell is doing.
1. Interphase – the non-dividing phase of the cell cycle.
a. G1 – This phase is when the cell is growing and maturing so it will be able to carry out its
function. The cell starts at half of its mature size, so it must grow and add organelles and
structures. The cell carries out its functions in this phase. For example, once a liver cell
matures it will produce digestive enzymes and detoxify the blood.
b. S – This is the phase when the cell replicates the chromosomes in the nucleus. Once the
cell moves into S phase it is committed to dividing as the chromosomes are unable to
function.
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c. G2 – This phase is when the cell carries out its final preparation for division. The
chromosomes condense into tight bundles to help with the separation of the copies of
the chromosomes into the two daughter cells. The cell also copies other cell
components, such as mitochondria and the cytoskeleton, to prepare for division and to
provide organelles for the daughter cells.
2. Division – this is also called M-phase or just Mitosis
The cell cycle has checkpoints to ensure that a cell is ready to proceed to the next stage. As the cell
moves through the cell cycle and it reaches a checkpoint, it will stop its activities until the cell is checked
to make sure it is in the right state to move forward. For example, when a cell reaches the checkpoint
between S and G2, the cell will be checked to make sure all of the chromosomes have been replicated
properly.
Prior to your lab period, view the animation of the cell cycle: http://www.cellsalive.com/cell_cycle.htm
Scenarios of when mitosis occurs in the human body
Mitosis occurs when our body needs to add more cells for growth and repair. We all started as a single
cell, the zygote, immediately after the sperm fused with the ovum, combining the chromosomes from
the father with chromosomes from the mother to produce a full set. As soon as the zygote formed, the
cell was signalled to grow and then divide, those daughter cells were also signalled to grow and divide.
This “grow and divide” process continued until there was a substantial number of cells, at which time
the cells begin to differentiate, to change and specialize, and the mass of cells became an embryo. As
the cells began to specialize and change, they continued to divide by mitosis in order to add more cells.
After the fetus was born, the cells in the body continued to divide by mitosis to allow the baby to grow
through all of the stages until adulthood when growth generally stops. Mitosis does not halt, however,
as our bodies are constantly being repaired due to daily damage.
There are four general phases of mitosis.
1. Prophase: this is a preparatory phase as the cell is getting structurally organized to separate the
chromatids. The cytoskeleton is getting organized and the nuclear membrane is breaking apart.
2. Metaphase: this is another preparatory phase as the chromosomes are getting organized in
such a way that the chromatids can be separated from each other. The chromosomes line up
end to end around the circumference of the cell. If you think of the cell as a globe, the
chromosomes are lined up end to end along the equator with one chromatid on the north side
and the other chromatid on the south side.
3. Anaphase: the chromatids are separated from each other and are moved by the cytoskeleton to
opposite ends of the cell.
4. Telophase: the cell begins to rebuild in preparation for the separation of the parent cell into two
daughter cells. The nuclear membranes are built around the two sets of chromosomes.
As mitosis is ending, during telophase, cytokinesis occurs to divide the parent cell into two daughter
cells. Whereas mitosis is the division of the copies of the chromosomes, cytokinesis is the physical
division of the parent cell. The resulting daughter cells immediately enter G1, the phase where they grow
and mature.
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Prior to your lab period, view the animation of mitosis: http://www.cellsalive.com/mitosis.htm
Scenarios of when meiosis occurs in the human body
At some point in the evolutionary history of life on earth, sexual reproduction evolved as a mechanism
to increase genetic diversity in a species, which is a good way to ensure survival of the species in an
ever-changing environment. Sexual reproduction is the fusion of chromosomes from one individual with
the chromosomes of another individual. In humans, as in most other organisms, the chromosomes
carried in the sperm (male) fuse with the chromosomes carried in the ovum (female).
Human body cells have a total amount of DNA, organized into 46 chromosomes of particular lengths.
This amount of DNA, organized in this particular way, is what defines us as the species Homo sapiens. It
is quite easy to see why a mechanism for reducing chromosome number in cells that are involved sexual
reproduction evolved if you think about it like this:
46 chromosomes from the sperm + 46 chromosomes from the ovum = 92 chromosomes in the zygote.
That zygote would not have the correct amount of DNA for a human.
Meiosis is the mechanism that reduces the chromosome number by half and only occurs in cells that will
become gametes, so in the testes of males and the ovaries of females. In order to accomplish the task of
reducing chromosome number, cells go through two genetic divisions to produce four daughter cells for
each parent cell.
The equation changes to look like this:
23 chromosomes from the sperm + 23 chromosomes from the ovum = 46 chromosomes in the zygote
To talk about these cells in general terms, not related to the chromosome number of any species, we
can use the terms haploid and diploid. Haploid cells have half the number of chromosomes as diploid
cells.
Haploid
gamete
23 chromosomes
diploid
zygote
46 chromosomes
Prior to the start of meiosis, all of the chromosomes are replicated, the chromosomes are condensed,
and the cell is readied for division. The phases of meiosis are very similar to the phases of mitosis, with
some key differences.
1. Prophase I: all of the same preparatory events occur as in mitosis. The biggest difference is that
the homologous chromosomes pair up and physically sit very close to each other in the cell.
When the pairs come physically close to each other this is called synapsis. Recall that the
chromosomes have been copied and each chromosome has two chromatids, therefore synapsis
forms tetrads. The chromosomes are so close to each other that segments from one
chromosome are exchanged with the other chromosome in a process called crossing over. This
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creates new combinations of genes that have never existed before, increasing the genetic
diversity of the species. Note that crossing over occurs between non-sister chromatids.
2. Metaphase I: in this phase the homologous chromosome pairs are organized so that the
homologous chromosomes can be separated from each other. The homologous chromosome
pairs line up end to end around the circumference of the cell, with one chromosome on each
side.
3. Anaphase I: the homologous chromosome pairs are separated as the cytoskeleton moves the
chromosomes apart to opposite ends of the cell.
4. Telophase I: the nuclear membranes are built around the groups of chromosomes. The parent
cell gets ready to divide into two daughter cells.
Cytokinesis occurs to physically separate the parent cell into two daughter cells. If you were to count the
chromosomes in these daughter cells, you would find there would be 23 chromosomes, one from each
of the pairs, and that each chromosome would still be copied, so would consist of 2 chromatids. At this
point, the daughter cells have the right number of chromosomes to be gametes, but each chromosome
has two chromatids, and the cell can’t function with chromatids. Meiosis II takes care of this:
5. Prophase II: The cytoskeleton is getting organized and the nuclear membrane is breaking apart.
6. Metaphase II: The chromosomes line up end to end around the circumference of the cell.
7. Anaphase II: the chromatids are separated from each other and moved by the cytoskeleton to
opposite ends of the cell.
8. Telophase II: the cell begins to rebuild in preparation for the separation of the parent cell into
two daughter cells. The nuclear membranes are built around the two sets of chromosomes.
Cytokinesis occurs to physically separate the parent cell into two daughter cells. If you were to count the
chromosomes in each of the four daughter cells, you would find each cell would have 23 chromosomes.
In summary, Meiosis I separates the homologous chromosomes and Meiosis II separates the chromatids.
At the end, there are four daughter cells that are not identical to the parent cell, or each other, because
synapsis and crossing over rearranged the genes on the chromosomes to make unique combinations.
Prior to your lab period, view the animation of meiosis: http://www.cellsalive.com/meiosis.htm
Spermatogenesis
Sperm are produced in the testes of human males. The male testes produce sperm on a fairly consistent
basis in order to maintain a constant supply of sperm. The process starts with diploid cells that divide by
mitosis to produce a stockpile of cells (primary spermatocytes) that can divide by meiosis to become
immature sperm. The immature sperm mature to become functioning sperm cells.
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Spermatogenesis
-
Streamlined
Motor + tail
Maturing
n
n
n
2n
Primary
Spermatocyte
n
n
Secondary
Spermatocyte
n
Spermatid
Sperm
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Oogenesis
In females, the process of producing ova begins in the fetal ovaries of the unborn girl. During fetal
development, mitosis occurs to produce a substantial number of cells that can become ova. Those cells
divide through meiosis I to produce haploid cells. During cytokinesis, after meiosis I and meiosis II, there
is unequal division of cytoplasm which produces one large daughter cell and one very small daughter
cell (the polar body). The process stops at that point and the haploid cells remain dormant in the ovaries
of the female as she develops through to early stages of puberty.
After meiosis occurs in the fetal ovaries, the secondary oocytes remain dormant in the ovaries of the
fetus, baby and child until the girl reaches puberty. Once the hormones that control puberty are
activated, a secondary oocyte is released from the ovaries on a schedule. If that secondary oocyte meets
with a sperm in the fallopian tube, the secondary oocyte quickly finished meiosis by dividing through
Meiosis II, creating another polar body (containing 23 chromatids) and an ovum (containing 23
chromatids). The chromatids from the ovum combine with the chromatids from the sperm to form the
zygote. If the secondary oocyte does not meet a sperm in the fallopian tube, it is shed out of the body
during menstruation. Secondary oocytes are released regularly from female ovaries from puberty until
menopause. Unequal division of cytoplasm puts most of the cell components into one daughter cell as
this is the cell that will become the ovum and form the cell that will be the zygote once the
chromosomes from the sperm combine with the chromosomes of the ovum. Creating as large a cell as
possible ensures the zygote has all of the cell resources it needs to start growing into the embryo
immediately after the zygote is formed.
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The complete picture
Sperm
n
n
Secondary
Oocyte
2n
n
Ovum
Secondary
Oocyte
n
2nd Polar
Body
n
Primary
Oocyte
Fusion of
nuclei
2n
Zygote
1st cell of
next
generation
1st Polar
Body
Fetal
Ovaries
Oogenesis halts until
puberty begins and
secondary oocytes are
released from mature
ovaries
Fallopian
tube
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Readings
In order to be able to complete your lab on time and get the most out of it, complete these readings and
view the videos or animations before your lab period.
o
o
o
o
o
o
o
o
Textbook Chapter 18
Textbook Chapter 16.2 and 16.3
DNA: http://www.hhmi.org/biointeractive/dna/DNAi_paired_strands.html
Chromosomes: http://www.hhmi.org/biointeractive/dna/DNAi_human_chromosomes.html
Cell Cycle: http://www.cellsalive.com/cell_cycle.htm
DNA replication: http://www.hhmi.org/biointeractive/dna/DNAi_replication_vo1.html
Mitosis http://www.cellsalive.com/mitosis.htm
Meiosis: http://www.cellsalive.com/meiosis.htm
Pre-lab Questions
1. What is the purpose of mitosis?
2. What is the purpose of meiosis?
3. Do you think organisms that reproduce by sexual reproduction are more successful, in an
evolutionary sense, than organisms that reproduce by asexual reproduction?
4. If you break a bone in your body how does your body heal that broken bone?
5. If all cells in the body have all of the chromosomes, how do parent cells provide chromosomes
for the daughter cells?
6. Why do human males have a constant supply of sperm?
7. Why do human females only release one or two secondary oocytes at a time?
8. Think about or look up how aquatic animals, such as salamanders, reproduce in terms of how
they produce gametes. Is it the same as humans?
9. What happens if meiosis does not occur correctly? Think about or look up non-disjunction of
chromosomes.
10. How do twins occur?
Lab activities and worksheets
Read through this section before you get to lab so you are aware of what you will be doing during the
lab period.
Replication
DNA is a macromolecule made up of smaller parts called nucleotides. A nucleotide is a molecule that is
made up of a phosphate, a sugar called deoxyribose, and a base. The base is the part that identifies the
nucleotide and it interacts with other bases to form the double helix of the chromosome. There are 4
different bases and they interact with each other in specific ways, based on their chemical structure. The
four bases are Adenine, Guanine, Cytosine, and Thymine. They interact with each following
complementary base pairing rules:
Adenine bonds with Thymine (A-T)
Guanine bonds with Cytosine (G-C)
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DNA is a double helix molecule. This means that there are two strands of nucleotides that are bonded
together (base to base) to form a ladder-like structure, which is then twisted into a helix, similar to a
spiral staircase where the banisters form the outside of the molecule and the steps are the bases
bonded together. If you want to try to make a double helix at home, you can cook spaghetti, separate
two strands and wrap them loosely around a paper towel tube, pinching them together at the top and
bottom. Once the spaghetti dries, pull or cut out the tube and you have a double helix. And supper!
View the ball and stick model of the double helix.
Inside of the nucleus, the enzymes that know how to read and copy DNA open up the double helix, read
each base and then pair it up with a corresponding base, making a whole new chromosome. The process
occurs very quickly in the nucleus, make copies of the chromosomes very quickly.
In the following table, practice replicating DNA. Using the given bases as a template, write in the bases
that would be matched to the given bases. The first two columns are the nucleotides of the original
chromosome. Through the process of replication, two chromatids will be formed. Each chromatid has an
original strand of nucleotides and a newly constructed complementary strand of nucleotides.
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This activity is a TA Checkpoint. Have your replicated DNA molecule checked and initialled by a lab
Teaching Assistant.
Original1 Original2
Original1 Complement1
Complement2 Original2
A T
A
T
T A
T
A
G C
G
C
G C
G
C
C G
C
G
C G
C
G
A T
A
T
C G
C
G
G C
G
C
T A
T
A
T A
T
A
A T
A
T
T A
T
A
C G
C
G
T A
T
A
T A
T
A
A T
A
T
C G
C
G
T A
T
A
A T
A
T
T A
T
A
C G
C
G
G C
G
C
A T
A
T
T A
T
A
A T
A
T
G C
G
C
The letters (nucleotides) that you wrote form the complementary strands of the new DNA molecules.
The letters that were given to you represent the original strands in the new DNA molecules. Because the
original strands always show up (are conserved) in the new molecules, replication is referred to as a
semi-conservative process.
Prior to coming to lab, view the video on DNA replication:
http://www.hhmi.org/biointeractive/dna/DNAi_replication_vo1.html
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Mitosis in the human body: Infection! White blood cells to the rescue!
About 5 days after Mary had gouged her hand while gardening she noticed that the wound was not
healing very well. The skin around the wound was red and hot and it generally hurt. Mary’s mother
decided that it was probably infected and made an appointment with the family doctor. The doctor
confirmed that, while Mary was protected against tetanus, she had probably picked up some other
common soil bacteria which then grew out of control and caused the infected state. The doctor
explained that the swelling and redness were a normal reaction of the immune system as the body tried
to fight off the infection in the wound. The bone marrow in the femur had received the signal that an
infection was brewing and that extra white blood cells (infection-fighting cells) were needed.
In the bone marrow are cells that can divide by mitosis to produce white blood cells. The way it works is
there is a stockpile of blood stem cells (S in the diagram below) that divide by mitosis, producing two
daughter cells. One daughter cell remains a stem cell and the other develops into the white blood cell
(or another kind of blood cell, if that is what is required).
S
S
Cell that becomes one of the blood cells
Prior to coming to lab, view the video on mitosis: http://www.cellsalive.com/mitosis.htm
Look at the posters of mitosis
Look at the models of mitosis
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View the slides of mitosis (onion root tip or whitefish blastula) and draw the phases of mitosis that you
can see. Divide up the phases in your group and have each person draw and explain one phase to the
rest of the group.
Prophase
Metaphase
Anaphase
Telophase
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The mitosis activity
(Adapted from: http://www.biologylessons.sdsu.edu/classes/lab8/lab8.html )
You are going to mimic the stages of mitosis as they occur in a unique organism called the Triffle (Latin
name Triffle triffle). A Triffle is a mythical creature with six chromosomes that look like knives, forks,
and spoons. You will work out each step of the process using yarn for membranes and plastic knives,
forks and spoons for chromosomes.
Replicate the steps in mitosis, starting with a cell that has received the signal to divide and is passing
from G1 into S.
Materials
o
o
o
o
Yarn – two pieces 100 cm in length
Yarn – two pieces 250 cm in length, a different colour than the 100 cm pieces
Rubber bands – 6
Fork, knives, spoon – 4, 2 each of 2 different colours
1. Cut yarn to represent the nuclear membrane and the cell membrane. Use one colour to
represent the nuclear membrane and cut two pieces 100 cm in length. Set one piece to the side.
Use a different colour to represent the cell membrane and cut two pieces that are each 250 cm
in length. The yarn for the cell membrane will be overlapped when you lay out your cell. As you
begin to move your chromosomes through the stages of mitosis, you can expand the cell.
2. Pick up 6 small rubber bands.
3. Begin with a cell and nucleus containing six chromosomes represented by two forks (one red &
one white), two knives (one red & one white), and two spoons (one red & one white). This
represents a diploid cell with three pairs of chromosomes. Note: you may have different colours
than what are listed here, but does not matter. It is important to have two different colours.
a. What would the arrangement of the cell be if the cell is in interphase?
4. The cell has moved through S phase.
a. What has happened to the chromosomes?
5. Use the rubber bands to attach the “chromatids” to each other. You should have two white
forks, two red forks, two white spoons, etc. The rubber bands represent the centromeres.
6. Your cell has passed from S to G2 and from G2 to mitosis. Follow the steps of mitosis, moving the
nuclear membrane and chromatids as they would move in a cell. Each person in the group
should do one phase and explain what is happening to the group. Repeat this until all members
of the group have explained all four stages of mitosis.
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7. Finish the process by creating two daughter cells. If you would like to draw your daughter cells
or any of the steps of mitosis, you can use the back of the page.
This activity is a TA Checkpoint. Show your lab TA the process of cell division starting in S phase.
Meiosis: And baby makes…92?
Remember that humans and other sexually reproducing organisms must produce gametes by meiosis in
order to avoid having a zygote with too many chromosomes.
Prior to coming to lab, view the video on meiosis: http://www.cellsalive.com/meiosis.htm
Look at the posters of meiosis
Look at the models of meiosis
The meiosis activity
(Adapted from: http://naturalsciences.sdsu.edu/classes/lab2.5/lab2.5.html#anchor29709092 )
You are going to mimic the stages of meiosis as they occur in a unique organism called the Piffle (Latin
name Piffle piffle). Piffle is a mythical creature with four chromosomes that look like clay. You will work
out each step of the process using yarn for membranes, and clay for chromosomes. The Piffle is a distant
relative of the Triffle from the mitosis exercise.
Materials
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Yarn – two pieces 100 cm in length
Yarn – two pieces 250 cm in length, a different colour than the 100 cm pieces
Clay – 2 different colours
1. Cut yarn to represent the nuclear membrane and the cell membrane. Use one colour to
represent the nuclear membrane and cut four pieces 100 cm in length. Set three pieces to the
side. Use a different colour to represent the cell membrane and cut four pieces that are each
250 cm in length. Set two pieces aside. The yarn for the cell membrane will be overlapped when
you lay out your cell. As you begin to move your chromosomes through the stages of meiosis,
you can expand the cell.
2. Use the clay to make 4 chromosomes, representing the diploid state of the cell as it exists in G1.
You will have 2 colours of clay, one colour representing the maternal chromosomes and one
colour representing the paternal chromosomes. For each colour, roll out 2 long chromosomes
and 2 short chromosomes. This is an easy way to differentiate the two homologous
chromosome pairs. The short pair is called Pair 1 and the long pair is called Pair 2.
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a. In what cells in the Piffle will meiosis take place?
b. Why the chromosomes in Pair 1 and in Pair 2 are called homologous?
3. The cell is moving from G1 to S phase. To mimic the replication of the chromosomes, roll out
identical snake-like pieces to the pieces you already have. Pinch the same colour, same length
pieces together to represent chromatids attached at the centromere. In your cell you will have 8
pieces of clay.
4. The cell is moving through G2 and into meiosis. Follow the steps of meiosis, moving the nuclear
membrane, homologous pairs and chromatids as they would move in a cell. Each person in the
group should do two phases and explain what is happening to the group. Repeat this until all
members of the group have explained all eight stages of meiosis.
a. How will you represent synapsis?
b. How will you represent crossing over?
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c. Between what chromosomes does crossing over take place?
i. Sister chromatids?
ii. Homologous chromosomes?
iii. Non-homologous chromosomes?
5. Once you have moved through all 8 phases of meiosis as well as cytokinesis, you will have four
daughter cells. If you would like to draw your daughter cells or any of the steps of meiosis, you
can use the back of the page.
6.
This activity is a TA Checkpoint. Show your TA the steps of meiosis and then initialled by a
lab Teaching Assistant.
7. When you are done, you can put your nuclear membrane yarn in the plastic bag labelled Nuclear
Membrane. You can put your cell membrane yarn in the plastic bag labelled Cell Membrane.
Separate the colours of clay and put them in the appropriate bag.
Lab assessments
In lab
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Results of practice replication
Daughter cells after mitosis and meiosis
Homework
- Study concepts using study guide
Study guide
1. Define mitosis. Explain how mitosis is the cell division that is used for growth and repair of
tissue.
2. Define meiosis. Explain what kinds of cells are produced by meiosis.
3. Describe how mitosis and meiosis are different from each other. (see background information)
4. Explain what a chromosome is and how many human body cells have.
5. Explain the 4 characteristics of homologous chromosomes.
6. Define DNA replication and briefly explain the steps of the process.
7. Explain how chromosomes and chromatids are different from each other.
8. Explain the phases of interphase.
9. Explain how the cell knows when to move through the cell cycle. (checkpoints)
10. Explain the four phases of mitosis.
11. Explain cytokinesis.
12. Explain why meiosis evolved as sexual reproduction evolved. In other words, why do organisms
that reproduce by sexual reproduction have to create their gametes by meiosis?
13. Explain the phase of meiosis. Include definitions of synapsis, tetrad, and crossing over.
14. How does crossing over increase genetic diversity in a species?
15. Explain the process of spermatogenesis.
16. Explain the process of oogenesis. Include definitions of polar body and unequal division of
cytoplasm.
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Bibliography
Cell cycle checkpoint. (2011, August 7). In Wikipedia, The Free Encyclopedia. Retrieved 16:02, August 11,
2011, from http://en.wikipedia.org/w/index.php?title=Cell_cycle_checkpoint&oldid=443522069
Nature 432, 316-323 (18 November 2004) | doi:10.1038/nature03097; Published online 17 November
2004
Spermatogenesis. (2011, August 5). In Wikipedia, The Free Encyclopedia. Retrieved 19:53, August 11,
2011, from http://en.wikipedia.org/w/index.php?title=Spermatogenesis&oldid=443121039
Oogenesis. (2011, August 7). In Wikipedia, The Free Encyclopedia. Retrieved 20:23, August 11, 2011,
from http://en.wikipedia.org/w/index.php?title=Oogenesis&oldid=443450109
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