Download Lab 8: Chromosomes and the Cell Cycle

Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
Lab 8: Chromosomes and the Cell Cycle
Introduction
In order for organisms to grow, replace moribund cells, repair tissue damage or reproduce
asexually, cells must divide, producing cells that are genetically identical to the original cell.
This type of cell division is called mitosis. For instance, in human cheek cells, such as those you
examined in an earlier lab, each cell has 46 chromosomes. When that cell divides via mitosis,
each of its daughter cells has 46 chromosomes. Maintaining this number is essential for genetic
continuity. If our cells did not have 46 chromosomes after division, they would not function
properly or they would die outright. An exception to this does exist, however, in meiosis.
The cell cycle is divided into interphase plus the stages of mitosis: prophase, metaphase,
anaphase and telophase. (Refer to Campbell or any handouts your instructor gives you for
illustrations.)
In interphase, the DNA found in chromatin replicates itself but does not completely
separate, it being held in double-DNA units by structures called kinetochores at regions called
centromeres. Most cellular growth and activity occurs during interphase, which may be divided
into a G1 phase, S phase and G2 phase. In G phases, cell growth occurs. In the S phase DNA
replication occurs. Since chromosomes are not supercoiled hence are not visible in interphase,
the nucleus stains lighter than in the other stages of the cell cycle; further, you should be able to
clearly see the nucleus and the darkly-stained nucleolus within the nucleus.
In prophase, the chromatin supercoils and becomes visible as darkly-stained, fingershaped bodies called chromosomes. Pay attention to the chromosomes as they will be the
clearest and most evident structure within the dividing cell. In prophase, the chromosomes are
completely disorganized. In animal cells, the centrosomes will have divided into centrioles and
will begin to form the mitotic apparatus of asters and spindle fibers; although plant cells do
have asters and spindle fibers they do not have centrosomes or centrioles.
In metaphase, in animal cells, the centrioles have migrated to either side of the cell. In
all cells, including plant cells, the chromosomes will have clearly lined up at the center of the
cell in an imaginary area called the equatorial plate. Because of this line of darkly-stained
chromosomes, this is the most evident stage of mitosis.
Anaphase is defined as being the stage when the kinetochores divide, separating the
double chromosomes of two chromatids into single chromosomes of one chromatid each.
Accompanying this is a lengthening of the dividing cell.
In telophase, the chromosomes have completed their migration to opposite ends of the
elongated cell. You should also see the beginning of a wall dividing the cells into two daughter
cells.
Cell division actually involves two processes: karyokinesis and cytokinesis. In
karyokinesis, the DNA replicates, chromosomes supercoil and divide, and the nucleus divides.
In cytokinesis, the rest of the cell, ie. the cytoplasm, divides.
The purpose of this lab is to examine and identify the various stages of mitosis in
prepared slides Allium (onion) root tips and in cells from Leucoichthyes (whitefish) and Ascaris
(roundworm).
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Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
Laboratory Objectives
After mastery of this laboratory, including doing the assigned readings and required
laboratory work, the student should be able to:
1. State the functions of mitosis.
2. Observe, identify, draw and label all stages of the cell cycle in commercially-prepared slides
of plant (Allium) and animal (Leucoichthyes and Ascaris) material.
3. Calculate the percentage of time plant (Allium) and animal (Leucoichthyes) cells spend in
each stage of the cell cycle (interphase, prophase, metaphase, anaphase and telophase) and
compare them.
Materials & Methods
~Allium
It is best to start your identification of the stages of the cell cycle with a good slide of the
root tip of Allium (onion) as it is the easiest to identify the stages in this material. Remember to
begin with the lowest power (4x objective, 40x total magnification) on your microscope. Focus
on cells near the tip of the root. Note that the cells occur in neat rows. Move the objective up to
the next highest power (10x objective, 100x total magnification) and refocus. Finally, use 400x
then 1000x total magnification. Pay close attention to the finger-like structures stained darkest
within each cell; these are the chromosomes. Identify each stage of the cell cycle. In your lab
report, draw each stage of the cell cycle while you observe it in the corresponding circles. Make
sure you identify the stages and note that they are from Allium. Draw what you see as you see it
in lab; you may not make drawings of what you observed some time after you made the
observations! You must include an accurate size rule AND obtain your instructor’s signature for
each drawing for credit.
On one or more of your drawings, draw lines to and label each of the following
structures:
chromosomes
cell wall
nucleolus
nucleus
Before you put the Allium root tip slide back, calculate the duration of each mitotic stage.
While examining the slide under 430x or 1000x total magnification, beginning at the top of one
of the rows of cells, identify the stage of the cell cycle that a particular cell is in. With your lab
partner serving as recorder, call out that stage. Go to the next cell down, identify and call out the
stage. Repeat this procedure until you have identified approximately 100 cells; if you like, do the
first 50 cells, then have your lab partner do the second 50.
When you finish collecting your data, sum up the total number of cells you counted and
place that number to the right of the (the Greek capital letter “sigma”, mathematical shorthand
for “sum”). Then calculate the percent of the total for each stage by dividing the number of each
stage by the total and multiply by 100. This number is equivalent to the average percent of time a
cell remains at that stage within the cell cycle. Record all of your data in your lab report.
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Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
~Leucoichthyes
Obtain a Leucoichthyes (whitefish) blastodisc slide from the demo table. Go through the
same procedure as above for Allium, finally examining the individual cells at 1000x total
magnification. Remember to begin with the lowest power. Note that the cells are stained
somewhat lighter than in Allium and are pinkish in color. You will have to carefully and patiently
use your fine focus to see the parts of Leucoichthyes cells, but spend some time on this. Again,
pay particular attention to the darkly-stained chromosomes as they define what stage of the cell
cycle the cells are in. Remember that there are no visible chromosomes in interphase! Identify
each stage of the cell cycle. In your lab report, draw each stage of the cell cycle while you
observe it in the corresponding circles. Make sure you identify the stages and note that they are
from Leucoichthyes. Draw what you see as you see it in lab; you may not make drawings of what
you observed some time after you made the observations! You must include an accurate size rule
AND obtain your instructor’s signature for each drawing to receive credit.
For one or more of your drawings, draw lines to and label each of the following
structures:
chromosomes
aster fibers
nucleus
spindle fibers
nucleolus
centrosome
When you are finished with your Leucoichthyes slide, put it back on the demo table for
someone else to use!
Calculate the average percent of time each cell spends in each of the stages of the cell
cycle with your Leucoichthyes slide, using the same protocol as with Allium, but using a smaller
sample size-thirty cells should be sufficient.
~Ascaris
Obtain a slide of Ascaris (roundworm) developing embryos from the demo table. Go
through the same procedure as for Allium and Leucoichthyes, finally examining the individual
cells at 1000x total magnification. Note that the cells are somewhat smaller than in Leucoichthes;
concentrate on finding the chromosomes. Again recall that there are no visible chromosomes in
interphase! You will have to carefully and patiently use your fine focus to see the parts of
Ascaris cells, but spend some time on this. Identify each stage of the cell cycle. In your lab
report, draw each stage of the cell cycle while you observe it in the corresponding circles. Make
sure you identify the stages and note that they are from Ascaris. Draw what you see as you see it
in lab; you may not make drawings of what you observed some time after you made the
observations! You must include an accurate size rule AND obtain your instructor’s signature for
each drawing to receive credit.
For one or more of your drawings, draw lines to and label each of the following
structures:
chromosomes
aster fibers
nucleus
spindle fibers
nucleolus
centrosome
When you are finished with your Ascaris slide, put it back on the demo table for someone
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Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
else to use; you do not have to count the numbers of cells in each phase for Ascaris.
Make sure you cleanup your work station, clean all equipment you used
and put it back, and help in general to keep the lab clean and in order!
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Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
Biol 160
Lab 8: Chromosomes and the
Cell Cycle
Prelab
(5 points)
Name: ___________________________________
Date: ________________ Lab Section: ________
~Complete this prelab before coming to lab; it is due at the beginning of lab!
1. According to the introduction to this lab, what are the functions of mitosis?
2. Give the visible characteristics would allow you to identify each of the phases of the cell
cycle:
a. Interphase:
b. Prophase:
c. Metaphase:
d. Anaphase:
e. Telophase:
3. What is karyokinesis?
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Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
4. What is cytokinesis?
8.6
Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
Biol 160
Lab 8: Chromosomes and the
Cell Cycle
Lab Report
(20 points)
Name: ___________________________________
Date: ________________ Lab Section: ________
~Allium
Results and Analysis
1. Drawings of the stages of the cell cycle (interphase, prophase, metaphase, anaphase and
telophase) of Allium, with cells labeled with chromosomes, nucleus, cell wall, nucleolus.
Magnification: _______________
Field of View: _______________
Rule = _________________ m
Identification of Drawing:
_________________________________
_________________________________
_________________________________
Instructor’s signature: _______________________
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Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
Magnification: _______________
Field of View: _______________
Rule = _________________ m
Identification of Drawing:
_________________________________
_________________________________
_________________________________
Instructor’s signature: _______________________
Magnification: _______________
Field of View: _______________
Rule = _________________ m
Identification of Drawing:
_________________________________
_________________________________
_________________________________
Instructor’s signature: _______________________
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Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
Magnification: _______________
Field of View: _______________
Rule = _________________ m
Identification of Drawing:
_________________________________
_________________________________
_________________________________
Instructor’s signature: _______________________
Magnification: _______________
Field of View: _______________
Rule = _________________ m
Identification of Drawing:
_________________________________
_________________________________
_________________________________
Instructor’s signature: _______________________
2. Numbers and percentages of Allium cells in each of the stages of the cell cycle.
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Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
Allium
N
%
Interphase
Prophase
Metaphase
Anaphase
Telophase
~Leucoichthyes
Results and Analysis
3. Drawings of the stages of the cell cycle (interphase, prophase, metaphase, anaphase and
telophase) of Leucoichthyes, with cells labeled with chromosomes, nucleolus, nucleus, aster
fibers, spindle fibers, centrosome.
Magnification: _______________
Field of View: _______________
Rule = _________________ m
Identification of Drawing:
_________________________________
_________________________________
_________________________________
Instructor’s signature: _______________________
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Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
Magnification: _______________
Field of View: _______________
Rule = _________________ m
Identification of Drawing:
_________________________________
_________________________________
_________________________________
Instructor’s signature: _______________________
Magnification: _______________
Field of View: _______________
Rule = _________________ m
Identification of Drawing:
_________________________________
_________________________________
_________________________________
Instructor’s signature: _______________________
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Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
Magnification: _______________
Field of View: _______________
Rule = _________________ m
Identification of Drawing:
_________________________________
_________________________________
_________________________________
Instructor’s signature: _______________________
Magnification: _______________
Field of View: _______________
Rule = _________________ m
Identification of Drawing:
_________________________________
_________________________________
_________________________________
Instructor’s signature: _______________________
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Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
4. Numbers and percentages of Leucoichthyes cells in each of the stages of the cell cycle.
Leucoichthyes
N
%
Interphase
Prophase
Metaphase
Anaphase
Telophase
~Ascaris
Results
5. Drawings of the stages of the cell cycle (interphase, prophase, metaphase, anaphase and
telophase) of Ascaris, with cells labeled with chromosomes, nucleolus, nucleus, aster fibers,
spindle fibers, centrosome.
Magnification: _______________
Field of View: _______________
Rule = _________________ m
Identification of Drawing:
_________________________________
_________________________________
_________________________________
Instructor’s signature: _______________________
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Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
Magnification: _______________
Field of View: _______________
Rule = _________________ m
Identification of Drawing:
_________________________________
_________________________________
_________________________________
Instructor’s signature: _______________________
Magnification: _______________
Field of View: _______________
Rule = _________________ m
Identification of Drawing:
_________________________________
_________________________________
_________________________________
Instructor’s signature: _______________________
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Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
Magnification: _______________
Field of View: _______________
Rule = _________________ m
Identification of Drawing:
_________________________________
_________________________________
_________________________________
Instructor’s signature: _______________________
Magnification: _______________
Field of View: _______________
Rule = _________________ m
Identification of Drawing:
_________________________________
_________________________________
_________________________________
Instructor’s signature: _______________________
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Putman’s Biol 160 Lab 8: Chromosomes and the Cell Cycle
Discussion
1. What was the longest stage of the cell cycle? What percentage of the cell cycle did the cells
you studied spend in this stage?
2. Why do you think a cell needs to spend so much time in the stage of the cell cycle you gave
in question 1?
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