Mitosis Lab
Pre Lab Questions (answer on a separate sheet):
1. What are the 4 “letter” phases of the cell cycle?
2. What happens during each “letter” phase of the cell cycle?
3. What are the 5 phases of cell division & what two things are dividing?
4. What happens in the 5 phases of cell division?
5. What are all the parts needed for cell division (think organelles, chromosome, etc.)?
6. What are the terms used to makes new cells & divide chromosomes?
Mitosis -- How Your Body Makes New Cells
How many cells do you think your body has?
Why does your body need to have lots of cells?
The production of such a large number of body cells is accomplished by many, many repeats of a cycle
of cell division in which one cell gives rise to two cells, each of which in turn gives rise to two cells, etc.
Thus, cell division is needed for growth.
Even in a fully grown adult, cells still undergo cell division. Why is this useful? For example skin cells.
The two cells that come from the division of one cell are called daughter cells. (It may seem odd, but
the cells produced by cell division are called daughter cells, even in boys and men.) Each of the
daughter cells needs to have a complete set of chromosomes. What are chromosomes? Why does each
cell need a complete set of chromosomes?
In each cycle of cell division, the cell first makes a copy of the entire DNA in each of the chromosomes,
as shown in the figure below.
After the DNA in each chromosome has been copied, the cell undergoes a type of cell division called
mitosis, which carefully separates the two copies of each chromosome to opposite ends of the dividing
cell, so each daughter cell ends up with a complete set of chromosomes.
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Mitosis -- The Basics
Once the DNA of a chromosome has been copied, the two copies of the DNA form two chromatids
which are attached to each other at the centromere. These chromatids are often called sister
chromatids because they are identical. (The two attached chromatids are called sister chromatids, even
in the cells of boys and men.) During mitosis the two chromatids of a chromosome separate and become
independent chromosomes; one of these chromosomes goes to each daughter cell.
Chromatids
Cell
Chromosome
Cell
Chromosomes
Cell 1
Cell 2
To keep things simple, we will begin by discussing mitosis in a cell which has only two chromosomes.
These two chromosomes are a pair of homologous chromosomes. Both homologous chromosomes
contain genes which control the same traits (e.g. eye color and skin color). For each gene on a pair of
homologous chromosomes, there may be two different versions or alleles of the gene on the two
different homologous chromosomes (e.g. an allele for brown eyes on one chromosome and an allele for
blue eyes on the other chromosome). This difference in alleles is indicated in the diagram on page 2 by
the stripe on each chromatid of the second homologous chromosome.
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Lab Experiment
Introduction:
Students will model cell growth, mitosis and cytokinesis using gummy worms, skittles, twizzlers and
yarn to represent the cell parts. Each chromosome will have two gummy worms joined at the middle to
represent the sister chromatids in a chromosome after the DNA has been replicated. The pair of gummy
worms will look like the chromosomes in the diagram on page 2.
Materials:
A. Two gummy worms of each color (6 total) – these are the chromosomes or chromatids
B. A string of twizzlers - these are the spindles
C. Four skittles – these are the centrioles
D. Two pieces of black string – these are the cell membranes
Procedure:
1. To indicate that you have a pair of homologous chromosomes, both gummy worms will be the same
color. Explain what the color represents, in terms of what it is for in the body. Students can get creative
with this – pick a trait for chromosomes to represent (brown hair, blue eyes, widows peak, etc.)
2. Together with the lab partner, use the cell parts to demonstrate how the cell grows in interphase - by
going through the phases of the cell cycle – G1, S, G2 and M. Form each stage with the candy and
draw it on the lab sheet on page 6 and LABEL all the parts, describe what is happening!.
3. Then with the lab partner, use the cell parts to demonstrate how the cell begins to divide in mitosis &
cytokinesis - by going through the phases of sister chromatids of each chromosome separate during
mitosis and become separate chromosomes, one of which goes to each daughter cell. Form each stage
with the candy parts and draw each stage and LABEL all the parts, describe what is happening!
*Make sure each phase is drawn on pages 5 & 6 before answering the post-lab questions!
Mechanics of mitosis
In a living cell, when the cell is carrying out its normal activities, the DNA molecule of each
chromosome is a long tangled thread. Each human cell has 46 chromosomes (23 pairs of homologous
chromosomes). Obviously, it would be difficult to reliably separate the two copies of each of 46 long
tangled DNA molecules. Therefore, in preparation for mitosis, the DNA is condensed into compact
chromosomes, like those shown in the diagram on page 2.
The basic steps of mitosis, which ensure that each daughter cell receives a complete set of
chromosomes, are as follows.
1. DNA is copied (called replication).
2. DNA is condensed into compact chromosomes (each with two sister chromatids); these are easier to
move than the long tangled DNA. Spindle fibers which will move the chromosomes begin to form.
3. Spindle fibers line the chromosomes up in the middle of the cell.
4. Spindle fibers shorten to pull the sister chromatids apart toward opposite ends of the cell.
5. The cell begins to pinch in half, with one set of chromosomes in each half.
6. Two daughter cells are formed.
For each of the figures below, give the number of the corresponding stage described above. Draw
arrows to indicate the sequence of events during mitosis. (For simplicity, the figures show cells that
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have only 4 chromosomes (2 pairs of homologous chromosomes), but the basic process is the same as in
human cells which have 46 chromosomes.)
Analysis: - Post Lab Questions on Mitosis
1. Are the chromosomes the daughter cells produced by mitosis the same as or different from the
chromosomes in the original cell? Explain.
2. What happens if a cell did not make a copy of its DNA (its chromosomes) before it divided?
3. Why is it important for the chromosomes to line up in the middle of the cell during mitosis?
4. In a mitosis ready cell, why are the two chromatids of each chromosome genetically identical?
5. Are the two homologous chromosomes genetically identical? Why or why not?
6. What was discovered about how a cell grows or divides in the cell cycle & mitosis/cytokinesis?
7. What “chromosomes” were involved in the experiment and why?
8. Which phase was the hardest or took the longest to make and why?
9. Which phase was the most fun to make and why?
10. What was learned during this lab and what did or did not work?
Conclusion:
- What went wrong or right during the lab? What worked or did not work?
- What did the lab need to be better?
After completing this lab, the materials may be eaten and a full lab write-up is required.
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