Lab 5 Cell Division

 

Objectives

After successful completion of the lab, students should be able to:

• Determine whether a cell is haploid or diploid
• List and describe the phases of mitosis
• Identify cells in the various phases of mitosis using the microscope
• Quantify the number of cells in the various phases of mitosis
• Calculate the percentage of cells that are actively dividing
• Relate the rate of cell division to cancer
• List and describe the phases of meiosis
• Compare and contrast meiosis and mitosis

Lab Reading

Cell Division

Diploid cells (2n) have two sets of chromosomes.  Haploid cells (1n) contain only one set of chromosomes.  In humans, egg and sperm are haploid.  All of our other somatic (body) cells are diploid.  Each eukaryotic species has a characteristic number of chromosomes For example, humans have 46 chromosomes in our diploid cells, while fruit flies of the genus Drosophila have only 8.  Salamanders have 24, chimpanzees have 48, and dogs and chickens both have 78.  While 78 chromosomes is a lot, some species of ferns have over 1,200 chromosomes in the nucleus of each of their cells!  The amount of chromosomes in the haploid cells of each species is half as much.  For humans, our haploid cells have 23 chromosomes while fruit flies have just 4 chromosomes in their haploid cells.

Mitosis and meiosis are two forms of cell division in eukaryotic cells.  Mitosis is a form of cell division in which one cell, the parent cell, divides to produce two new cells, the daughter cells.  Daughter cells in mitosis have the same number of chromosomes as the parent cell. Meiosis is a form of cell division that produces daughter cells with one-half the number of chromosomes as the parent cell.  That is, the mother cell is diploid (2n) and the daughter cells are haploid (1n).  Meiosis occurs in cells that will ultimately become gametes.  Gametesinclude eggs and sperm, the sex cells of sexually reproducing organisms.

The processes of mitosis and meiosis are often grouped together in the same discussion even though the two have very different functions.  The primary function of mitosis is the growth and cell replacement in an organism.  The primary function of meiosis is to produce haploid cells from diploid organisms for the purpose of sexual reproduction.  The two processes are often discussed together because of their mechanical similarities.

The Cell Cycle and Mitosis

As a human, you are comprised of trillions of cells that are all descendants of a single cell, the zygote (fertilized egg).  Mitosis is involved in the development of an adult organism from a zygote.  Mitosis is also involved in growth and repair oftissues, in regenerationof bodyparts, and in asexual reproduction. The parent cell produces two genetically identical daughter cells. Mitosis can occur in both diploid and haploid cells, depending on the type of organism.  If a diploid cell carries out mitosis, the daughter cells will be diploid.  If a haploid cell carries out mitosis, the daughter cells will be haploid?

Cell division is part of the cell cycle: the life of a cell from its origin until its own division into two daughter cells.  Interphase can be divided into three phases: G₁ phase (“1^st gap”), S phase (DNA synthesis phase), and G₂ phase (“2^nd gap”).  During these three subphases, the cell is also growing by producing proteins and organelles.  The cell grows during the “gap” phases, and copies its chromosomes during the S phase in preparation for cell division (mitosis and cytokinesis).Interphase alternates with mitosis; interphase accounts for approximately 90% of a cell’s life cycle.  The M phase, which includes mitosis and cytokinesis, is usually the shortest portion of the cell cycle (approximately 10% of a cell’s life).  Mitosis refers to the division of the nucleus only, and cytokinesis refers to the division of the cytoplasm (everything else the daughter cell needs).  Mitosis itself is typically broken down into five stages (in order): prophase, prometaphase, metaphase, anaphase, and telophase.

Mitosis in Animal versus Plant Cells

In animal cells, cytokinesis occurs by a process called cleavage.  The first sign of cleavage is the appearance of a cleavage furrow, which begins as a shallow groove in the cell surface near the metaphase plate—it looks like the cell is being squeezed in the middle.  The cleavage furrow divides the cell into two.   In plant cells, cytokinesis occurs with the formation of a cell plate.  The cell plate divides one plant cell into two.  This is because plants have a rigid cell wall.

This image shows the growing root tip of an onion.  Examples of cells in the various stages of mitosis and the cell cycle are labeled for you.

In this lab, you will be counting cells in mitosis in a prepared microscope image in order to compare the rate of cell division in mutant cells to normal cells.  During the stages of mitosis, the chromosomes are highly visible.  Any cells in which the chromosomes are not visible are not in the M phase and must be in Interphase (G1, S or G2).  The nucleus of a cell contains nucleoli—these are dark round spots with the nucleus.  Sometimes there are a couple of them, but they are not condensed chromosomes that show prophase is occurring.  The picture on the following page shows some examples of nucleoli.  Use the picture to practice to practice counting.  Prophase and Prometaphase are difficult to distinguish with a light microscope, so they have been combined into one box.  Note that you should focus on what is happening to chromosomes since the spindle apparatus is not visible with light microscopy.

 

 

 

 

 

 

 

 

 

 

 

Based on this image , you can see an example of data that that can be collected.  Note that when counting cells in images, there is some subjectivity.  For example, some people might call late anaphase early telophase instead.  A small amount of variation in the data is therefore expected.  Based on my data table, 40% of the cells are actively dividing, which is a relatively high rate of cell division.  You will create a similar table and analysis in the lab assignment.

Table: Number and percent of cells in various stages of the Cell Cycle

	Stage	# of cells counted in each phase in the view	% cells in each phase
Not actively dividing	Interphase	18	60
Mitosis, actively dividing	Prophase/Prometaphase	4	13.4
	Metaphase	1	3.3
	Anaphase	6	20
	Telophase	1	3.3
	TOTAL in Mitosis, actively dividing	12	40
	Total overall (cells in mitosis + cells in Interphase), should add up to 100%	30	100

 

Meiosis

Meiosis is the division of diploid (2n) parent cells to produce gametes (in animals and some plants) or spores (in fungi and other plants).  Gametes and spores will ultimately give rise to new individuals. Meiosis includes two rounds of divisions (Meiosis I and Meiosis II), unlike mitosis in which the nucleus divides only once. The parent cell in meiosis produces four haploid (n) daughter cells, each with one half of the chromosomes of the parent cell.  Therefore, all of the daughter cells are genetically different from the parent cell.

Each parent cell has pairs of homologous chromosomes, one inherited from the father (paternal) and one inherited from the mother (maternal). In meiosis, the maternal and paternal chromosomes are put into the daughter cells in many different combinations.  In humans, there are 2²³ (~ 8.4 million) possible combinations.  Meiosis ensures genetic variation in the offspring of sexually reproducing organisms. Genetic variation comes from crossing over, which occurs during prophase I of meiosis and unique combinations in the way the chromosome pairs line up during Metaphase I.  Genetic variation in populations is necessary for the process of natural selection and evolution to occur.

 

 

Lab Assignments and Procedures

 

Comparing the rate of cell division in normal cells versus cells with a mutation

 

This activity will ask you to analyze a microscope image of cells that carry a mutation to determine how many cells are actively dividing (in mitosis).  You will then compare your measurements to cells that do not have the mutation and predict the impact on cancer risk.  We will use the same basic format as other labs–I have outlined the experimental question and procedure for you.   For the write up, please copy and paste the remaining part of the Lab document into a new document, then fill in with your responses and images.  I have highlighted where a response is needed in yellow.  Submit your completed write up to the Dropbox.

 

Experimental Question:  How will a mutation affect the rate of cell division compared to cells without the mutation?

 

Predictions related to the experimental question:

What effect will mutations that promote cancer have on cell division—will they speed up cell division or slow it down?  Explain your reasoning.

Experimental design and procedures:

1. A micrograph of cells that have a mutation has been provided. You will analyze this picture for your data and graph.  Make sure you have read the Lab Reading section for helpful advice and an example of counting.

 

 

2. Tally the phase that each cell is in (Interphase or Mitosis: Prophase/Prometaphase, Metaphase, Anaphase or Telophase) by making hash marks on a s piece of paper. Prophase and Prometaphase are difficult to distinguish with a light microscope, so they have been combined into one category.
3. Add up the numbers from each phase; then fill in the appropriate column in the first Data table
4. Then use the following formula to calculate the percent of cells in each phase and fill in Table 2.1.

% = (# cells in phase/total # cells counted) X 100

5. Then, determine the % of activelydividing cells (only the ones in mitosis, not Interphase) by adding up the amount of cells in all of the phases of mitosis.
6. Record the % actively dividing cells in the second data table for the mutant sample and compare it to a normal sample. The number of cells that are actively dividing in normal tissue without the mutation has been provided for you in the table.  The normal sample had 0.1% of cells in mitosis.
7. Graph the % cells in mitosis in your mutant specimen and in a normal specimen.

 

Results

Data Table 1 .  Number and percent of cells in various stages of the Cell Cycle

	Stage of Cell Cycle	# of cells counted in each phase in the view	% cells in each phase
Not actively dividing	Interphase (not in Mitosis)
Mitosis, actively dividing	Prophase/Prometaphase
	Metaphase
	Anaphase
	Telophase
	TOTAL in Mitosis, actively dividing  (this is the value that goes into Table 2)
	Total overall (cells in mitosis + cells in Interphase), should add up to 100%

Table 2

Specimen	% actively dividing cells (cells in mitosis)
Normal (normal gene present), data provided	0.1%  (data from other colleagues, page 11 )
Mutant (mutant gene present), your data

 

 

Digital Graph—You are graphing the data from Table 2.  Remember to follow graphing guidelines from Lab 1.

 

 

Identify the variables in the experiment

Independent variable: 

Dependent variable: 

 

 

Summarize your results in words, making sure to describe the actual data: 

 

 

 

Conclusion and Discussion— Based on your data, what percentage of the mutant cells were actively dividing?  Is that more or less than normal cells?  How could you improve the design of this experiment to improve the accuracy of your data?  An abnormally high rate of mitosis is associated with cancer.  Based on this knowledge and using your data, how do you think this mutation might affect the chances that an individual with this mutation will get cancer.  Make sure to explain your answer.  Use APA format to cite any sources you consult.

 

Lab 5 Cell Division

 

Objectives

After successful completion of the lab, students should be able to:

• Determine whether a cell is haploid or diploid
• List and describe the phases of mitosis
• Identify cells in the various phases of mitosis using the microscope
• Quantify the number of cells in the various phases of mitosis
• Calculate the percentage of cells that are actively dividing
• Relate the rate of cell division to cancer
• List and describe the phases of meiosis
• Compare and contrast meiosis and mitosis

Lab Reading

Cell Division

Diploid cells (2n) have two sets of chromosomes.  Haploid cells (1n) contain only one set of chromosomes.  In humans, egg and sperm are haploid.  All of our other somatic (body) cells are diploid.  Each eukaryotic species has a characteristic number of chromosomes For example, humans have 46 chromosomes in our diploid cells, while fruit flies of the genus Drosophila have only 8.  Salamanders have 24, chimpanzees have 48, and dogs and chickens both have 78.  While 78 chromosomes is a lot, some species of ferns have over 1,200 chromosomes in the nucleus of each of their cells!  The amount of chromosomes in the haploid cells of each species is half as much.  For humans, our haploid cells have 23 chromosomes while fruit flies have just 4 chromosomes in their haploid cells.

Mitosis and meiosis are two forms of cell division in eukaryotic cells.  Mitosis is a form of cell division in which one cell, the parent cell, divides to produce two new cells, the daughter cells.  Daughter cells in mitosis have the same number of chromosomes as the parent cell. Meiosis is a form of cell division that produces daughter cells with one-half the number of chromosomes as the parent cell.  That is, the mother cell is diploid (2n) and the daughter cells are haploid (1n).  Meiosis occurs in cells that will ultimately become gametes.  Gametesinclude eggs and sperm, the sex cells of sexually reproducing organisms.

The processes of mitosis and meiosis are often grouped together in the same discussion even though the two have very different functions.  The primary function of mitosis is the growth and cell replacement in an organism.  The primary function of meiosis is to produce haploid cells from diploid organisms for the purpose of sexual reproduction.  The two processes are often discussed together because of their mechanical similarities.

The Cell Cycle and Mitosis

As a human, you are comprised of trillions of cells that are all descendants of a single cell, the zygote (fertilized egg).  Mitosis is involved in the development of an adult organism from a zygote.  Mitosis is also involved in growth and repair oftissues, in regenerationof bodyparts, and in asexual reproduction. The parent cell produces two genetically identical daughter cells. Mitosis can occur in both diploid and haploid cells, depending on the type of organism.  If a diploid cell carries out mitosis, the daughter cells will be diploid.  If a haploid cell carries out mitosis, the daughter cells will be haploid?

Cell division is part of the cell cycle: the life of a cell from its origin until its own division into two daughter cells.  Interphase can be divided into three phases: G₁ phase (“1^st gap”), S phase (DNA synthesis phase), and G₂ phase (“2^nd gap”).  During these three subphases, the cell is also growing by producing proteins and organelles.  The cell grows during the “gap” phases, and copies its chromosomes during the S phase in preparation for cell division (mitosis and cytokinesis).Interphase alternates with mitosis; interphase accounts for approximately 90% of a cell’s life cycle.  The M phase, which includes mitosis and cytokinesis, is usually the shortest portion of the cell cycle (approximately 10% of a cell’s life).  Mitosis refers to the division of the nucleus only, and cytokinesis refers to the division of the cytoplasm (everything else the daughter cell needs).  Mitosis itself is typically broken down into five stages (in order): prophase, prometaphase, metaphase, anaphase, and telophase.

Mitosis in Animal versus Plant Cells

In animal cells, cytokinesis occurs by a process called cleavage.  The first sign of cleavage is the appearance of a cleavage furrow, which begins as a shallow groove in the cell surface near the metaphase plate—it looks like the cell is being squeezed in the middle.  The cleavage furrow divides the cell into two.   In plant cells, cytokinesis occurs with the formation of a cell plate.  The cell plate divides one plant cell into two.  This is because plants have a rigid cell wall.

This image shows the growing root tip of an onion.  Examples of cells in the various stages of mitosis and the cell cycle are labeled for you.

In this lab, you will be counting cells in mitosis in a prepared microscope image in order to compare the rate of cell division in mutant cells to normal cells.  During the stages of mitosis, the chromosomes are highly visible.  Any cells in which the chromosomes are not visible are not in the M phase and must be in Interphase (G1, S or G2).  The nucleus of a cell contains nucleoli—these are dark round spots with the nucleus.  Sometimes there are a couple of them, but they are not condensed chromosomes that show prophase is occurring.  The picture on the following page shows some examples of nucleoli.  Use the picture to practice to practice counting.  Prophase and Prometaphase are difficult to distinguish with a light microscope, so they have been combined into one box.  Note that you should focus on what is happening to chromosomes since the spindle apparatus is not visible with light microscopy.

 

 

 

 

 

 

 

 

 

 

 

Based on this image , you can see an example of data that that can be collected.  Note that when counting cells in images, there is some subjectivity.  For example, some people might call late anaphase early telophase instead.  A small amount of variation in the data is therefore expected.  Based on my data table, 40% of the cells are actively dividing, which is a relatively high rate of cell division.  You will create a similar table and analysis in the lab assignment.

Table: Number and percent of cells in various stages of the Cell Cycle

	Stage	# of cells counted in each phase in the view	% cells in each phase
Not actively dividing	Interphase	18	60
Mitosis, actively dividing	Prophase/Prometaphase	4	13.4
	Metaphase	1	3.3
	Anaphase	6	20
	Telophase	1	3.3
	TOTAL in Mitosis, actively dividing	12	40
	Total overall (cells in mitosis + cells in Interphase), should add up to 100%	30	100

 

Meiosis

Meiosis is the division of diploid (2n) parent cells to produce gametes (in animals and some plants) or spores (in fungi and other plants).  Gametes and spores will ultimately give rise to new individuals. Meiosis includes two rounds of divisions (Meiosis I and Meiosis II), unlike mitosis in which the nucleus divides only once. The parent cell in meiosis produces four haploid (n) daughter cells, each with one half of the chromosomes of the parent cell.  Therefore, all of the daughter cells are genetically different from the parent cell.

Each parent cell has pairs of homologous chromosomes, one inherited from the father (paternal) and one inherited from the mother (maternal). In meiosis, the maternal and paternal chromosomes are put into the daughter cells in many different combinations.  In humans, there are 2²³ (~ 8.4 million) possible combinations.  Meiosis ensures genetic variation in the offspring of sexually reproducing organisms. Genetic variation comes from crossing over, which occurs during prophase I of meiosis and unique combinations in the way the chromosome pairs line up during Metaphase I.  Genetic variation in populations is necessary for the process of natural selection and evolution to occur.

 

 

Lab Assignments and Procedures

 

Comparing the rate of cell division in normal cells versus cells with a mutation

 

This activity will ask you to analyze a microscope image of cells that carry a mutation to determine how many cells are actively dividing (in mitosis).  You will then compare your measurements to cells that do not have the mutation and predict the impact on cancer risk.  We will use the same basic format as other labs–I have outlined the experimental question and procedure for you.   For the write up, please copy and paste the remaining part of the Lab document into a new document, then fill in with your responses and images.  I have highlighted where a response is needed in yellow.  Submit your completed write up to the Dropbox.

 

Experimental Question:  How will a mutation affect the rate of cell division compared to cells without the mutation?

 

Predictions related to the experimental question:

What effect will mutations that promote cancer have on cell division—will they speed up cell division or slow it down?  Explain your reasoning.

Experimental design and procedures:

1. A micrograph of cells that have a mutation has been provided. You will analyze this picture for your data and graph.  Make sure you have read the Lab Reading section for helpful advice and an example of counting.

 

 

2. Tally the phase that each cell is in (Interphase or Mitosis: Prophase/Prometaphase, Metaphase, Anaphase or Telophase) by making hash marks on a s piece of paper. Prophase and Prometaphase are difficult to distinguish with a light microscope, so they have been combined into one category.
3. Add up the numbers from each phase; then fill in the appropriate column in the first Data table
4. Then use the following formula to calculate the percent of cells in each phase and fill in Table 2.1.

% = (# cells in phase/total # cells counted) X 100

5. Then, determine the % of activelydividing cells (only the ones in mitosis, not Interphase) by adding up the amount of cells in all of the phases of mitosis.
6. Record the % actively dividing cells in the second data table for the mutant sample and compare it to a normal sample. The number of cells that are actively dividing in normal tissue without the mutation has been provided for you in the table.  The normal sample had 0.1% of cells in mitosis.
7. Graph the % cells in mitosis in your mutant specimen and in a normal specimen.

 

Results

Data Table 1 .  Number and percent of cells in various stages of the Cell Cycle

	Stage of Cell Cycle	# of cells counted in each phase in the view	% cells in each phase
Not actively dividing	Interphase (not in Mitosis)
Mitosis, actively dividing	Prophase/Prometaphase
	Metaphase
	Anaphase
	Telophase
	TOTAL in Mitosis, actively dividing  (this is the value that goes into Table 2)
	Total overall (cells in mitosis + cells in Interphase), should add up to 100%

Table 2

Specimen	% actively dividing cells (cells in mitosis)
Normal (normal gene present), data provided	0.1%  (data from other colleagues, page 11 )
Mutant (mutant gene present), your data

 

 

Digital Graph—You are graphing the data from Table 2.  Remember to follow graphing guidelines from Lab 1.

 

 

Identify the variables in the experiment

Independent variable: 

Dependent variable: 

 

 

Summarize your results in words, making sure to describe the actual data: 

 

 

 

Conclusion and Discussion— Based on your data, what percentage of the mutant cells were actively dividing?  Is that more or less than normal cells?  How could you improve the design of this experiment to improve the accuracy of your data?  An abnormally high rate of mitosis is associated with cancer.  Based on this knowledge and using your data, how do you think this mutation might affect the chances that an individual with this mutation will get cancer.  Make sure to explain your answer.  Use APA format to cite any sources you consult.