OBSERVATION OF MITOSIS
Comments and Suggestions
(in order to conserve space, I used single spacing, but you should ALWAYS double space)
(you should also have provided a table with your TYPED results)
Questions
Please type out your answers to these questions. (answers should be COMPLETE sentences!) Multiple pages must
be stapled together (no paper clips or unattached pages). You do not have to include the actual question, but please
number your answers. Don’t forget to include the above table!
1. Which cell cycle phase requires the longest time for completion?
It depends on your data, but typically it is Interphase.
Comment:cell cycle consists of Interphase, Mitosis, and Cytokinesis.
2. Which mitotic phase requires the longest time for completion?
It depends on your data, but typically it is Prophase.
Comment:as stated above – Interphase is NOT part of mitosis
3. What important changes are occurring in the nucleus during the longest phase of mitosis? Does this
justify
the amount of time spent in the phase?
Several events occur that might be expected to extend the time necessary for completion of prophase. For
example, the spindle apparatus must form and the chromosomes condense. (See the textbook/notes for
more.)
4. Which mitotic phase requires the next longest time for completion?
It depends on your data.
5. Which mitotic phase requires the shortest time for completion?
It depends on your data.
6. Are there any assumptions made in using this method to estimate the timing of phases within the cell
cycle?
What are the most important assumptions?
Two assumptions are that: 1) the areas selected are samples that represent the true distribution of cell
stages; 2) there was no bias in distinguishing the cell stages (there was no tendency to mistake one stage
for another).
Comment: note that assumptions are not outcomes (results). You should make no assumptions about
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your results. Make assumptions only about the methods used to collect your data, or that are necessary to
create testable hypotheses.
7. Which mitotic phase for normal cells requires the longest time for completion?
For this data, prophase is the longest mitotic phase. (Interphase is not a stage of mitosis.)
8. How do cancer cells differ from normal cells in time spent for each cell cycle phase?
You could compare the fraction of time spent in each phase for the cancerous cells compared to the
normal cells. This is:
Interphase: 2/15
Prophase: 1/4
Metaphase: 1/5
Anaphase: 1/3
Telophase: 1/4
Interestingly the differences are not the same for all phases (they are disproportionate). However, the
sample size is small.
9. How do cancer cells differ from normal cells in total time required for mitosis?
Mitosis has a shorter duration in cancer cells than in normal cells. For these data, mitosis occurs in 21
minutes in cancerous cells and 85 minutes in normal cells.
10. What are your hypotheses?
One option could be:
H0: There is no difference in the total duration of the cell cycle in cancerous stomach cells compared to
normal stomach cells.
HA: There is a difference in the total duration of the cell cycle in cancerous stomach cells compared to
normal stomach cells.
These data could allow you to test other complementary hypotheses. Another option could be:
H0: The duration of phases of mitosis change proportionately in cancerous stomach cells compared to
normal stomach cells.
HA: The duration of phases of mitosis change disproportionately in cancerous stomach cells compared
to normal stomach cells.
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11. Given the data presented here, what conclusion can you make about your hypotheses?
There is a difference in the total duration of the cell cycle in cancerous stomach cells compared to
normal stomach cells.
OR
The duration of phases of mitosis change disproportionately in cancerous stomach cells compared to
normal stomach cells.
12. Imagine you decide you want to publish the results of your (this) research. What are some important
assumptions made in this study that you might need to defend in your written work?
Two assumptions are that: 1) cancerous cells of chicken stomachs are representative of other types of
cancerous cells; 2) there was no bias in distinguishing the cell stages (there was no tendency to mistake
one stage for another).
Comment: note that assumptions are not outcomes (results). You should make no assumptions about
your results. Make assumptions only about the methods used to collect your data, or that are necessary
to create testable hypotheses.
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