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?

2. Pre-lab Questions:

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?

The sperm fertilizes the egg, and creates a zygote. The zygote then undergoes mitosis several times, it divides about to become a morula, and then a blastocyst, which will have the inner cell mass which are undifferentiated and create the baby. It takes about 37 mitotic cell division for a zygote to grow into an organism with 100 trillion cells.

2. How is cell division important to a single-celled organism?

Cell division is important to a single-celled because that's how the organism reproduces itself. By reproducing, the chromosomes and genes will be kept in the population.

3. What must happen to ensure successful cell division?

To ensure successful cell division, the cell must go through the stages of the cell cycles, G1, S, G2, and mitosis. To divide into daughter cells, it needs to replicate the organelles and DNA, without mistakes. In order for there to not be mistakes in the DNA, it then must go through the checkpoints to make sure the cell has functioning parts and the correct DNA to be divided to the daughter cells.

4. How does the genetic information in one of your body cells compare to that found in other body cells?

Genetic information in on of our body cells is the same to any other cell in our body. Our DNA is being replicated throughout the cycle, what makes each cell different is what tells that cell to differentiate into. What makes our cells different are transcription factors, which turn on specific parts of the cell to differentiate it.

5. What are some advantages of asexual reproduction in plants?

Asexual reproduction in plants is an advantage so it can just reproduce its own cells without a mate, this makes it easier for the plant to replicate its genes. If those genes are successful in the environment, then it will keep reproducing, which can be an advantage by quickly reproducing for the environment.

6. Why is it important for DNA to be replicated prior to cell division?

It is important for DNA to be replicated prior to cell division because then there will be two sets of DNA for each daughter cell. By replicating the DNA before, then each daughter cell will have the proper DNA, which is needed for it survive and to pass down the genes.

7. How do chromosomes move inside a cell during cell division?

Chromosomes move inside a cell during cell division during mitosis. The mitotic spindles are attached to the kinetochores, if not attached then it can not continue cell division. Once it's attached the spindle fibers will pull the chromosomes at opposite poles of the cell, which is pulling the chromosomes into the two daughter cells.

8. How is the cell cycle controlled? What would happen if the control were defective?

The cell cycle is controlled by checkpoints and complexed made up of specific proteins. These complexes contain enzymes called cyclin-dependent proteins, (CDKs), which turn on or off various processes that take place during cell division. The cell must pass through three checkpoints, G1 checkpoint, G2 checkpoint, and the M-spindle checkpoint. Each checkpoint checks that the cell is ready for the next part of the cycle. If one of these controls were defective then the cell could divide abnormally, and grow out of control.

3. How is cell division controlled?

Cell division is controlled by checkpoints and specific proteins, such as cyclin-dependent proteins, and cyclins. These cyclin-dependent proteins (CDKs), turn on or off various processes that take place during cell division. But these cyclins aren't the only things controlling cell division, they are between the checkpoints. The cell must also go through three checkpoints, first growth stage (G1), second growth stage (G2), and the M-spindle. This is where each checkpoint makes sure the cell has done its needed task, and it ready to proceed to the next step without any errors in the DNA or cell. G1 checks for the appropriate external growth factors. G2 checks for damage in DNA replication, if there is it cannot go on. And M-spindle checks for the mitotic spindles to be properly attached to the kinetochores. If any error occurs the cell will try to repair it, or commits cell suicide, or apoptosis.

part one: modeling mitosis

4. How do eukaryotic cells divide to produce genetically identical cells?

In mitosis, eukaryotes divide to produce two genetically identical daughter cells. The chromosome replicates, creating a pair of sister chromatids. The sister chromatids are aligned in the middle of the cell by spindle fibers so then each daughter cell can receive one of the chromosomes. The sister chromatids are pulled apart at the centromere by centrioles at opposite poles of the cell. The sister chromatids separate, and the result of mitosis is two identical daughter cells with the identical chromosomes of the parent.

5. Page s87 Part 1 Questions:

1. If a cell contains a set of duplicated chromosomes, does it contain any more genetic information than the cell before the chromosomes were duplicated?

No, it does not contain any more genetic information than the cell before the chromosomes were duplicated because the cell only contains the genetic material that was replicated from the parent cell.

2. What is the significance of the fact that chromosomes condense before they are moved?

It is significant that the chromosomes condense before they are moved so during anaphase they can equally separate into the chromosomes for the two daughter cells.

3. How are the chromosome copies, called sister chromatids, separated from each other?

The sister chromatids are separated from each other by the spindle fibers pulling them at opposite poles of the cell to create the two daughter cells.

4. What would happen if the sister chromatids failed to separate?

If the sister chromatids failed to separate then the cell that didn't divide will have more chromosome compared to other cells, and this can lead to complications. Since the cell didn't do its task properly it would need to undergo cell suicide.

Part two: effects of environment on mitosis

6. Various fungi can negatively affect the growth of soybeans by producing a lectin-like protein. Lectins can induce mitosis in the root apical meristem tissue which will often weaken the plant tissue.

1. What is your experimental hypothesis? Your null hypothesis? Are these the same?

My experimental hypothesis will be adding lectins to the root tip will increase the number of cells in mitosis. My null hypothesis would be that adding lectins to the root tip will have no affect to the number of cells in mitosis. The experimental hypothesis and the null hypothesis are the opposites of each other.

2. How would you design an experiment with onion bulbs to test whether lectins increase the number of cells in mitosis?

I would have onion bulbs in lectins, and onion bulbs without lectins. I would keep both of them under the same conditions for the same period of time, and after that period is over I'd look at which had more cells undergoing mitosis, whether it was the onion bulbs exposed to lectins or not.

3. What would you measure, and how would you measure it?

I would measure the number of cells in each group, I would do this by looking at them under a microscope and by counting or noticing if the cells divided.

4. What would be an appropriate control for your experiment?

An appropriate control for my experiment would be onion bulbs without lectin present.

Null Hypothesis: A hypothesis which the researcher tries to disprove, reject or nullify.

Chi-squared Test: Any statistical hypothesis test in which the sampling distribution of the test statistic is a chi-square distribution when the null hypothesis is true.


Class Data:

Observed Values:

Expected Values:

8. Chi-squared calculations:

9. How to accept or reject the null hypothesis:

If the chi-square value is greater than or equal to the critical value, 3.84, then the null hypothesis is rejected. If it is less than 3.84, then the null hypothesis isn't rejected.

10. Should the null hypothesis be accepted or rejected? What does this mean in terms of your hypothesis?

The null hypothesis should be accepted because the class data results for the chi-squared value is .969. This is less than the critical value of 3.84 meaning that there is no significant difference.

Part three: loss of control of cell cycle

11. Post Lab Review:

1. What was the importance of collecting the class data?

The importance of collecting the class data was to collect as much information as possible to have more accurate calculations.

2.  Was there a significant difference between the groups?

There was no significant difference between the groups because the chi-square test proved the null hypothesis.

3.  Did the fungal pathogen lectin increase the number of root tip cells in mitosis?

The fungal pathogen lectin didn't increase the number of root tip cells in mitosis due to the statistical analysis of the data.

4. What other experiments should you perform to verify your findings?

Other experiments could be testing the fungal pathogen lectin on different plant roots to see if there is a difference in the number of root tip cells in mitosis.

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, it does indicate that the mitosis rate is faster when the number of cells is greater, the more cells, the more cells will undergo mitosis.

6. What other way could you determine how fast the rate of mitosis is occurring in root tips?

Another way that you can determine how fast the rate of mitosis is occurring in root tips is by  adding different amounts of lectin onto onion root tips and collecting the data for periods of time. If there is or isn't a difference due to the amount of lectin added, it will add accuracy to whether or not lectin does increase the number of cells in undergoing mitosis.

12. Case 2 Activity:

1. What happens in a normal cell if the DNA has mutations?

A mutation in the cell can occur when a base is inserted or deleted from the DNA sequence, once this occurs the codons would be different, creating different proteins than normal. Once this mutation occurs, the cell could be in danger since it has a different structure that will have a different function than normal, which can cause problems in the cell cycle.

2. What would happen if cells with mutated DNA replicated?

If cells with the mutated DNA is replicated, than that mutation will be in the daughter cells that are created in mitosis. More cells will have the error in the DNA and eventually those cells will undergo mitosis as well, spreading the mutation among the cells.

3. How do cells monitor DNA integrity?

The cell monitors DNA integrity through checkpoints in the cell cycle and cyclins and CDKs. These monitor the cell for any mistakes, and makes sure that the cell has been finishing its tasks. If the cyclins and CDKs find that the cell isn't prepared to grow and divide properly, then the cell will undergo apoptosis.

4. How are the chromosomes different in the cancer cells compared to normal cells?

Any difference in chromosomes in cancer cells compared to normal cells can be identified in a karyotype which examines a picture of a person's chromosomes. In normal cells, it has 23 pairs of chromosomes. In cancer cells, there would be more than a pair, it could range from 6 chromosomes to 20. This show that an error occurred during mitosis. Along with this the chromosomes will be shaped weirdly and in the karyotype, any difference in color can indicate that the chromosome is a mixture between other chromosomes.

5. How could these differences lead to cancer?

These differences, mutations and different chromosomes, can lead to cancer because any mutation in the DNA can mess up the function of the DNA, and different number of chromosomes show a failure in a cell when undergoing mitosis. If a mutation occurs, then the checkpoints and genes that regulate the cell won't be able to recognize the mistake, and the cell will grow and divide with those differences, making cancer spread.

13. Nondisjunction: The failure of homologous chromosomes or sister chromatids to separate properly during cell division. A result of nondisjunction is genetic diseases and abortions.

Part four: modeling meiosis

14. Chromosome models:

15. S93 Questions:

1. When is the DNA replicated during meiosis?

The DNA is replicated during the stage of interphase.

2. Are homologous pairs of chromosomes exact copies of each other?

Homologous pairs of chromosomes aren't exact copies of each other because one chromosome comes from the mother and the other chromosome comes from the father. The only exact copies are made when they duplicate.

3. What is crossing-over?

Crossing-over occurs when the homologous chromosomes align and pair up, the mother and father chromosomes can intertwine and wrap with one another. When this happens alleles can swap from mother to father, creating new chromosomes and different genetic material than the parent.

4. What physical constraints control crossover frequencies?

What controls crossover frequencies is how close together that homologous chromosomes are to one another. If they are close enough, then they can intertwine and swap alleles. If they aren't close together than the chromosomes can't wrap around, and crossing-over won't take place.

5. What is meant by independent assortment?

When the chromosomes align in the middle of the cell, it is at random, or independent assortment. One side can have more of the mother's chromosomes and lesser amount of the father's chromosomes, this will add genetic variation.

6. How can you calculate the possible number of different kinds of gametes?

You can calculate the possible number of different kinds of gametes by multiplying together the number of genes there are for each parents and determin the number of combinations.

7. 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?

Nondisjunction occurs when homologous pair of chromosomes fail to separate properly during cell division. A cell can have more than 2 pairs of chromosomes, or less than. Down Syndrome occurs in chromosome pair 21, when the chromosome failed to separate, and results in three chromosomes, or a trisomy. Cri du chat syndrome happens when part of chromosome pair 5 is deleted.

8. How are mitosis and meiosis fundamentally different?

Mitosis and meiosis are different when comparing the number of division, daughter cells, and how the chromosomes align up. Mitosis has one division, while meiosis has two, meiosis I and meiosis II. This results into having only two identical daughter cells in mitosis, and four daughter cells in meiosis. Also before separation, the chromosomes in mitosis align in an independent matter, while in meiosis they align up in homologous pairs.

part five: meiosis and crossing over

16. Lab Bench Activity

17. S96 Evaluating Results Questions:

1. Why did you divide the percentage of asci showing crossover (recombinant) by 2?

I divided the percentage of asci showing crossover by 2 because the the spores that crossed over were only half.

2. The published map distance between the spore color gene and the centromere is 26 map units. How did the class data compare with the distance?

The class data was 31.8 map units while the published map distance was 26 map units, a difference of 5.8 map units.

3. How can you account for any disparities between the class data and the published data?

Any disparities between the class data and the published data could have occurred due to incorrect spores being counted or because the class data didn't have a huge collection of data, meaning an in precise average.

4. Illustrate what happened during meiosis to produce the results you found.

What happened during meiosis to produce the results was crossing-over. When the homologous chromosomes paired up, they were close enough to wrap around one another and swap alleles. This created the different results in the spores in the activity.

5. Do you think the Philadelphia chromosome is a result of crossing over as seen in this part of the investigation or some other chromosomal abnormality? Explain your answer.

I don't think the Philadelphia chromosome is a result of crossing over because of the shorter and longer lengths of the chromosomes. Instead of crossing over, something had to go wrong, such as translocation, or when the chromosomes rearrange part or drift off to another chromosome.

6. Do you think the cell cycle described for mitosis could be applied to meiosis as well? Explain your answer.

The cell cycle described for mitosis can't be applied to meiosis as well. This is due to the results of how many daughter cells are created at the end, in mitosis 2 daughter cells, and in meiosis, 4 daughter cells. Both have similar steps such as replication, alignment, and separation, but they chromosomes undergo those steps in two distinct ways.

Comment Stream