Lab 7-Cell Division: Mitosis and Meiosis
by Sambavi Prakasam


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


1. I developed from a single celled zygote to an organism with trillions of cells through the process of the cell cycle. which includes the phases: interphase, mitosis, and cytokinesis. My cells continuously went through this cycle in order for my zygote to develop into an organism. It would take 5x10^11 mitotic cell divisions in order for a single zygote to become an organism.

2. Cell division is important to a single-celled organism because it allows the organism to divide and pass on its genetic information to the next generation

3. In order for their to successful cell division, the cell must undergo a series of checkpoints. These three checkpoints are known as the G1 checkpoint, the G2 checkpoint, and the M-spindle checkpoint.

4. The genetic information in one body cell relates to the genetic information of another body cell in they way that they are both identical, as long as the genetic information did not mutate when it was copied.

5. An advantage in asexual reproduction of plants is that it allows them to create new chloroplasts through binary fission. It also allows the plant to create cells it may require as well.

6. It is important for DNA to be replicated prior to cell division, so that during the G2 checkpoint, the cyclins and CDKs can make sure that the DNA is not damaged or mutated.

7. Chromosomes move in a "V" shape as they are pulled apart by spindle fibers in the cell during cell division.

8. The cell cycle is controlled by complexes that are composed of several specific proteins which are known as cyclin-dependent kinases(CDKs). If the control were defective, then the CDKs may not turn on or off the various processes the cell undergoes during the cell cycle.

Controlling Cell Division

The cell cycle is controlled by complexes made up of several specific proteins. These complexes are known as cyclin-dependent kinases (CDKs), which regulate when various processes in the cell cycle are turned on or off. CDK works with proteins called cyclins. The CDK is activated when it is bound to the cyclin, which allows the cell to proceed from G1 into mitosis. The levels of cyclin vary throughout the cell cycle.

Part 1: Modeling Mitosis

How do eukaryotic cells divide to produce genetically identical cells?

Eukaryotic cells divide to produce genetically identical cells by first going through the G1 phase where the chromosomes un-condense and become straight in order to for the chromosome to be copied. The cell then goes through the S phase where the chromosome is copied and is composed of sister chromatids, and is essentially shaped like an "X". The cell then goes through mitosis where the sister chromatids are separated from each other so that each chromosome will eventually go to one of the two daughter cells. The cell then goes through the final stage of cytokinesis where the one of the chromosomes ends up in one of the two daughter cells and the chromosomes condense again.

1. If a cell contains a set of duplicated chromosomes, it contains double the amount of the same genetic information than before the chromosomes were duplicated in the cell.

2. Chromosomes condense before they are moved because it helps them separate easily during mitosis. Also, it helps when chromosomes need to be transported, and lowers the chance that the molecule will break or mutate.

3. Sister chromatids are separated from each other by being pulled apart by spindle fibers which separate the chromosomes in a "V" shape.

4. If the sister chromatids failed to separate, then there would be double the amount of chromosomes than a normal cell, within that cell.

Part 2: Effects of Environment on Mitosis

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.

My experimental hypothesis is that the fungal protein lectin does affect the number of cells undergoing mitosis in the root tips. My null hypothesis is that lectin does not affect the number of cells undergoing mitosis in the root tips.

An experiment that could be used to test this is to place two onion tips each in separate containers. One container can have lectin solution in it and the other container can be the control with water in the container. After continuously looking at the onion tips for a week the total amount of data collected can be compiled.

This could be measured by examining the number of cells in the onion tip under a microscope, and checking to see whether more cells have appear to undergo mitosis over a period of time.

A control for the experiment could be to not apply any lectin to the container with the water.


null hypothesis- a general statement or default position that establishes that there is no relationship between two measured phenomena; by rejecting or disproving the null hypothesis, there is proof that there is a relationship between the two quantities that are being measured; it is assumed that a null hypothesis is to be true until evidence proves otherwise

chi-squared test- aka the x^2 test; is used when the null hypothesis is true; is a statistical hypothesis test; used to determine of there is a significant difference between the expected frequencies and the observed frequencies in one or more categories

Class Data

Observed and Expected Values

The null hypothesis is accepted when calculated chi-square value is less than the critical value on the chart. The null hypothesis is rejected when the chi-square value that is calculated, is greater than or equal to the critical value.

The null hypothesis is accepted, which means that lectin does not affect mitosis in the onion root tips. This mean that the hypothesis has been proven false since it shows that lectin does not affect mitosis in onion root tips.


1. The importance of collecting the class data is to have a bigger group of data that consists of multiple trials, which makes the data more accurate to rely on and also provides more statistics for testing.

2. No there was not a significant difference between the expected and observed groups as there was only a difference of 11 cells, while we had counted a total of about 3,000 cells.

3. No, the fungal pathogen lectin does not affect the number of root tip cells undergoing mitosis because the null hypothesis was accepted.

4. Another experiment that could be performed is to place different amounts of lectin solution in separate containers with onion root tip to see if a greater amount of lectin will precipitate an increase in the number of cells undergoing mitosis in the onion root tip.

5. An increased number of cells in mitosis does not mean that these cells are dividing faster than the cells in the root tip with a lower number of cells in mitosis, it could just mean that the root tip needed to regenerate more cells than the other root tip needs at this time.

6. Another way to determine the rate at which mitosis occurs in root tips is to count the number of cells undergoing mitosis one day, count the cells undergoing mitosis the next day in the same sample, and continue counting for a week for example, and then use the number of cells undergoing mitosis in total to determine the rate by dividing by the number of days that the root tips were measured for.

Part 3: Loss of Control of Cell Cycle

1. A normal cell that has DNA that contains mutations will cause the cell to not function normally and the cell may or may not be able to complete certain tasks that may be necessary to the cell's company.

2. If the cells with mutated DNA replicated, then there would be more mutated cells as well as damaged DNA. This would allow the mutated DNA to spread and allow more faulty cells in the organism.

3. Cells monitor DNA integrity by using CDKs and cyclins, these proteins check to see if the DNA is has been damaged or severely mutated, which can prevent the cell from replicating

4. Chromosomes are different in cancer cells than in normal cells because they may be damaged or severely mutated that the chromosome may not be able to carry out its initial purpose.

5. The difference in the chromosomes of cancer cells is that it is easier for these cells to be infected by bacteria and diseases and infect the nucleus of the cell, than those of normal cells.

Nondisjunction is the failure of homologous chromosomes or sister chromatids failing to separate properly during cell division. This results in the daughter cell ending up with abnormal chromosome numbers. When the cell is fertilized, a number of syndromes can occur due to a monosomy (one chromosome missing) or trisomy(an additional chromosome is included with the other two).  

Part 4: Modeling Meiosis

1. DNA is replicated during interphase of meiosis.

2. Homologous pairs are not exact copies of one another as one chromosomes as one chromosome comes from the mother and the other chromosome comes from the father.  

3. Crossing over is the creation of recombinant chromosomes. Crossing over occurs when a piece from one chromosome breaks off and switches with another chromosome where the same piece breaks off, this creates a different frequency of an allele in the chromosome.

4. The closer the chromosomes are in proximity to each other the easier to is for the alleles to crossover. The farther the chromosomes are from each other the harder it is for the alleles to crossover. The distance between the chromosomes affects its ability to cross over.

5. Independent assortment is the way that the chromosomes line up in the cell with respect to the cell poles. The way that the chromosomes line up is completely random in the cell.

6. A way to calculate the possible number different kind of gametes is to multiply the total number of pairs of chromosomes by four(to represent the four daughter cells).

7. If a pair of homologous chromosomes fail to separate then a trisomy will be created, which means that the zygote will contain three of one type of chromosome. This leads to genetic disorders such as Down Syndrome and cri du chat syndrome since both of these diseases originate from a trisomy in the karyotype.

8.Mitosis creates somatic cells and only creates two daughter cells from the parent cell, while meiosis creates gametes and produces four daughter cells from the parent cell.

Part 5:Meiosis and Crossing Over

Analysis of Results (Lab Bench Activity)

Evaluating Results

1. The percentage od asci showing crossovers was divided by two because every crossover produces two spores, but the number must be divided by two because the only half the spores in each ascus result in crossing over.

2. The class data that was collected was 31.8 map units (see above for results in analysis of results), the class data was a little but longer than the distance of the published map distance of 26 map units.

3. The large difference between the class data and the published data can be attributed to the small number of asci that we looked at during class. If we had examined more samples, perhaps the frequencies would be closer.


5. The Philadelphia chromosome occurred as a result of the crossing over in this activity. This occurred because as a whole we were calculating the number of gametes we can create from crossing over alleles.

6, The cell cycle could be described using the same steps for mitosis for meiosis because both processes share the same "big idea" steps, replication, alignment, pairing up(meiosis), and separation.

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