Lab 7 - Cell Division: Mitosis and Meiosis
How do eukaryotic cells divide to produce genetically identical cells or to produce gametes with half the normal DNA?
1. How did you develop from a single celled zygote to an organism with trillions of cells? How many mitotic cell divisions would it take for one zygote to grow into an organism with 100 trillion cells?
A single celled zygote is able to develop to an organism with trillions of cells by using the process of mitosis. This process includes many different phases that allows for a cell to duplicate itself. Cells constantly undergoing this process are able to replicate extremely quickly and effectively causing the creation of trillions of cells. It takes trillions of mitotic divisions in order to cause 1 single cell to grow into a 100 trillion cell organism.
2. How is cell division important to a single celled organism?
Cell division is extremely important for a single celled organism because it allows for asexual reproduction.
3. What must happen to ensure successful cell division?
All of the phases of mitosis must be completed with no errors, in addition the DNA of an organism must be replicated accurately with no mutations that would lead to a change in proteins.
4. How does the genetic information in one of your body cells compare to that found in other body cells?
Genetic information is relatively the same throughout al the cells in a body. However certain cells specialize in different areas depending on their location in the body.
5. What are some advantages of asexual reproduction in plants?
Asexual reproduction allows for the same genetic code to be passed on throughout generations with little to no changes in the DNA.
6. Why is it important for DNA to be replicated prior to cell division?
DNA must be replicated prior to cell division so when the cell undergoes mitosis and splits, each cell has the right amount of chromosomes and not just half.
7. How do chromosomes move inside a cell during cell division?
Throughout the process of mitosis the chromosomes move depending on the phases. In the middle phases the chromosomes move toward the center of the cell and line up to prepare for the separation. During the actual split the chromosomes migrate towards the edges of the cells to ensure an equal division.
8. How is the cell cycle controlled? What would happen if the control were defective?
Cell division is controlled by the different phases throughout mitosis. The different phases control the split and duplication of the chromosomes. In addition, the division of cells is also controlled by CDK which are found in proteins. These enzymes allow for the cell to move through the different phases quickly and effectively with no errors. These enzymes make sure each phase is completed successfully before they allow the cell to move on to the next phase.
Eukaryotes divide using the process of mitosis in which chromosomes are replicated and are formed into sister chromatids, which are bonded in the centromere. CDKs move the cell along through this process and guide the cells through the different phases. In these phases the sister chromatids line up in the center of cell in order to divide evenly. Then the cell's chromosomes begin to migrate to opposite poles in order to create an even split. The cell then divides evenly into two daughter cells.
• If a cell contains a set of duplicated chromosomes, does it contain any more genetic information than the cell before the chromosomes were duplicated?
Yes, the cell contains double the amount of genetic information in the time in between the replication of DNA and the separation of the two new cells.
• What is the significance of the fact that chromosomes condense before they are moved?
This process allows for easier transport and DNA replication.
• How are the chromosome copies, called sister chromatids, separated from each other?
They are separated by the imaginary line that goes through the cell and sets the boundaries of the new two cells that are to be formed
• What would happen if the sister chromatids failed to separate?
The chromosomes would not equally distribute and the two new cells would become defective and go through apoptosis.
In order to test whether or not lectin has an effect on the rate of mitosis, we can look at different samples of root tip cells. We can put these samples in a lectin and water solutions to see if there is any noticeable difference in the mitosis rate.
A null hypothesis is a statement that is either rejected or accepted that disproves the hypothesis. A chi-squared test is used in experiments such as this in order to determine whether or not there is a difference between two different variables.
Null hypothesis accepted
1. What was the importance of collecting the class data?
To improve the accuracy by adding multiple different trials and examples.
2. Was there a significant difference between the groups?
No, there was no significant difference between the groups.
3. Did the fungal pathogen lectin increase the number of root tip cells in mitosis?
No, the lectin had no effect on the rate of mitosis in the root tip cells
4. What other experiments should you perform to verify your findings?
More degrees of the experiment should be performed in order to ensure accurate results and a conclusion.
5. Does an increased number of cells in mitosis mean that these cells are dividing faster than the cells in the roots with a lower number of cells in mitosis?
Yes, the amount of cells present indicate the speed mitosis is occurring
6. What other way could you determine how fast the rate of mitosis is occurring in the root tips?
Checking how many cells there are in the root tips at different times.
What happens in a normal cell if the DNA has mutations?
If a normal cell contains mutations, usually the cell will go through apoptosis and kill itself.
What would happen if cells with mutated DNA replicated?
If cells with mutated DNA replicated then the mutated trait would become prevalent in the body which would either be damaging or beneficial.
How do cells monitor DNA integrity?
Cells monitor DNA integrity by not allowing a cell to continue living and replicating if it contains a mutation.
How are the chromosomes different in cancer cells compared to normal cells?
The chromosomes are differently shaped and some look like they are missing vital genetic information
How could these differences lead to cancer?
Differences like these could lead to improper repair and growth which could cause the immune system to deteriorate and tumors to form.
Nondisjunction is when homologous pairs of sister chromotids fail to separate equally between the new cells. This results in many different disorders and also is the main cause of cancer.
Part 4. Modeling Mitosis and Meiosis
When is the DNA replicated during meiosis?
At the beginning of the process, similar to mitosis.
Are homologous pairs of chromosomes exact copies of each other?
No many times they are different and in result when the genetic information is switched between them, genetic variation occurs
What is crossing over?
Crossing over is what happens when genetic information between a pair of chromosomes is switched while the chromosomes are intertwined.
What physical constraints control crossover frequencies?
Multiple cross overs can only occur when genes are next to each other
What is meant by independent assortment?
Independent assortment means that the chromosomes do not line up in any particular order so they are split between the news cells randomly.
How can you calculate the possible number of different kinds of gametes?
By calculating the possible amount of chromosome combinations.
What happens if a homologous pair of chromosomes fails to separate, and how might this contribute to genetic disorders such as Down syndrome and cri du chat syndrome?
Cells carry extra chromosomes which replicates and makes more cells with extra genetic information which leads to overlapping instructions which causes these disorders.
How are mitosis and meiosis fundamentally different?
Mitosis aligns its chromosomes in a single line down the center where as meiosis has its chromosomes in pairings on different sides of the imaginary line in the cell. In addition, mitosis creates two identical sister cells and meiosis creates four different daughter cells.
Part 5: Evaluating Results
Why did you divide the percentage of asci showing crossover by 2?
To calculate the map distance.
How can you account for any disparities between the class data and the published data?
The samples were different and so were the sample sizes so that alone could account for error. In addition it is highly unlikely that the experiment was performed both times under the exact same conditions so that could also account for any disparities.
Do you think the Philadelphia chromosome is a result of crossing over as seen in the part of the investigation or some other chromosomal abnormality? Explain your answer
I think that the Philadelphia chromosome is due to another chromosomal abnormality because the sizes of the chromosome show equal lengths which would indicate that the crossing over process was a success
Do you think the cell cycle described for mitosis could be applied to meiosis as well? Explain your answer.
No because the cells in mitosis must be identical which would mean the color would not change and there would be no genetic variation.