Lab 7 - Cell Division: Mitosis and Meiosis

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How do eukaryotic cells divide to produce genetically identical cells or to produce gametes with half the normal DNA?

Pre-lab questions:

1.How did you develop from asingle-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?

I developed from a single-called zygote to an organism with trillions of cells due to the cell cycle and mitosis, which allowed the original cell to grow and divide into a human being. It would take a lot of mitotic cell divisions for one zygote to grow into an organism with 100 trillion cells.

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

Without it,the single-called organism would have no method of reproduction.

3. What must happen to ensure successful cell division?

All checkpoints must be reached and then the cell has to be at the right stage so it can pass the checkpoints and eventually divide.

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

It is the exact same, with the exception of sperm and egg cells.

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

All genetic information is passed to the next generation and it doesn't take as much energy.

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

It is important so each daughter cell gets a complete set of DNA.

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

The chromosomes are replicated and condensed in interphase. In metaphase they line up on the metaphase plate. In anaphase the chromosomes are pulled apart. They eventually reach the poles of the cell in telophase.

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

The cell cycle is controlled with regulatory proteins. An uncontrollable cell cycle can lead to cancerous cells.

#5

There are three checkpoints in the cell cycle that control cell division. They are the G1, G2, and Spindle Assembly checkpoints. These checkpoints are controlled by proteins (cyclins) and enzymes (CDKs). The G1 checkpoint checks for proper cell growth, nutrients, growth factors, and DMA damage. The G2 checkpoint checks for proper cell size and DNA replication. The Spindle Assembly checkpoint checks for proper chromosome attachment to the kinetochores. If the checkpoints see that everything is in order, the cell cycle moves onto the next step.

#6

How do eukaryotic cells divide to produce genetically identical cells?

The cells growand replicate their DNA in order to duplicate the chromosomes. The chromosomes line up towards the middle of the cell where spindle fibers attach to the centromeres. The sister chromatids are pulled apart, each containing an identical copy of the DNA. Nuclei begin to form around the sister chromatids and the cytoplasm divides, creating two identical daughter cells.

#7

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 because they have the exact same genetic information as the original chromosomes.

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

The significance of the chromosomes condensing is that they can be separated into equal halves in anaphase.

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

Spindle fibers attach to the sister chromatids and pull them to opposite sides of the cells.

What would happen if the sister chromatids failed to separate?

If the sister chromatids failed to separate one newly made cell would have more chromosomes than the other which would prevent the cells from functioning properly.

#8

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

In this situation, the experimental hypothesis and null hypothesis are opposites. My experimental hypothesis is that lectin will increase the amount of mitosis that will take place in the roots. My null hypothesis is that lectin will not increase the amount of mitosis that will take place in the roots.

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

You would take onion bulbs and soak one in a solution of water and one in a lectin solution. After letting them soak, you observe both onion roots under a microscope and count the number of cells in interphase and mitosis.

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

You would measure the number of cells in both the treated root and the control root. This would be done by examining the onion roots under the microscope and counting the number of cellin interphase and mitosis.

What would be an appropriate control for your experiment?

An appropriate control group would be an onion bulged soaked in water.

#9

Null hypothesis: the hypothesis that there is no significant difference between specified populations, any observed difference being due to sampling or experimental error

Chi square 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

X^2=sigma(o-e)^2/e

O is the observed value, x^2 is chi squared, and  e is the expected value.

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

The null hypothesis should be excepted because the chi squared value is .969. It is less than 3.84 which is the comparative value in this situation. In terms of my hypothesis this means that there is no significant difference between lectin and the amount of mitosis taking place in the roots.

11. Postlab Review:

What was the importance of collecting the class data?

The importance of collecting the class data was to have enough data points in order for the data to be valid.

Was there a significant difference between the groups?

There was not a significant difference between the groups.

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

Based on the statistical analysis, the fungal pathogen lectin does not increase the number of root tip cells in mitosis.

What other experiments should you perform to verify your findings?

Other experiments could include testing lectin on different plants or varying the amount of lectin exposed to the cells.

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?

An increased number of cells in mitosis does not necessarily mean that these cells are dividing faster than the cells in the roots with a lower number of cells in mitosis.

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

You could separate two sets of cells and expose one to lectin. Then you can time how long it actually takes for the cells to separate and see if there is any difference between them.

12. Case 2:

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

If the DNA has mutations the health of the cells will be endangered. The cell could become dangerous and potentially cancerous, leading to many complications.

What would happen if cells with mutated DNA replicated?

If the mutated DNA gets replicated, it will spread to other cells once mitosis occurs. This creates even more cells with the mutated DNA. The spreading of it could get out of control.

How do cells monitor DNA integrity?

Cyclins and CDKs check the cell at certain points to ensure that the cell is growing and dividing normally. If normal growth is not occurring, the cell with go through apoptosis,

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

Karyotypes of cancer cells and normal cells vary greatly. Normal cells have 23 pairs of homologous chromosomes. Cancer cells can have more than 6 or 7 chromosomes that are grouped together, rather than just two normally. The chromosomes can also be abnormally shaped.

How could these differences lead to cancer?

These differences can lead to cancer because the mutated DNA may not be able to control the cell cycle. If this is the case, proto-oncogenes and tumor suppressor genes will not be able to regulate the cell cycle and uncontrollable cell growth will occur, leading to tumors.

13. Nondisjunction- The failure of homologous chromosomes or sister chromatids to separate properly during cell division. It can cause genetic diseases such as Down Syndrome and Turner Syndrome, as well as spontaneous abortions.


15. When is the DNA replicated during meiosis?

The DNA is replicated during interphase.

Are homologous pairs of chromosomes exact copies of each other?

They are not exact copies of each other. One chromosome comes from the mother and one comes from the father,

What is crossing over?

Crossing over occurs in meiosis when homologous chromosomes pair up. The chromosomes wrap around each other and sometimes swap alleles. This swapping is the process of crossing over.

What physical constraints control crossover frequencies?

The physical constraint that controls crossover frequencies is distance. The closer and more wrapped together the chromosomes are, the more likely crossing over is to occur. The opposite is the case for when the chromosomes are father from each other.

What is meant by independent assortment?

Independent assortment is how the chromosomes line up on the metaphase plate. Their order is completely random which increases genetic variation.

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

You multiply the number of genes by the number of alleles.

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?

If a homologous pair of chromosomes fails to separate nondisjunction occurs. This can result in monosomy and trisomy. Cells with either have too many, or too little, chromosomes. Down Syndrome is also called trisomy 21. The homologous chromosome pair 21 fails to separate, resulting in trisomy. Cri du chat occurs when part of chromosome 5 is deleted. The result is monosomy. The abnormal amount of chromosomes are the cause of genetic disorders.

How are mitosis and meiosis fundamentally different?

Mitosis has one division and meiosis has two. Mitosis results in two identical daughter somatic cells and meiosis results in four different daughter gametes.


17. Evaluating results:

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

I divided the percentage of asci showing crossover by two since only half the spores in each as us result from crossing over.

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

The class got 31.8 map units, 5.8 units away from the published map distance.

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 make have occurred because of random chance, incorrect counting due to a lack of clarity in the slide, and a small sample size.

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

Crossing over occurred to produce the results that I found. Crossing over happens when homologous chromosomes pair up and they get so close together that they swap alleles. Because of this process, it allowed me to find the results that I found.

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 think the Philadelphia chromosome is a result of failed crossing over. Translocation ,as have occurred which explains why one chromosome appears shorter and one appears longer.

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

No. The end results for mitosis and meiosis are very different so it is unlikely that the cell cycles are regulated in the same manner.

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