Lab 7 - Cell Division: Mitosis and MeiosisHow do eukaryotic cells divide to produce genetically identical cells or to produce gametes with half the normal DNA? #NPAPBio

#2 Prelab Questions:

1. There are many cell divisions that develop a simple zygote into a complex organism.  It would take 47 mitotic cell divisions for a zygote to grow into a an organism with 100 trillion cells.

2. Cell division is the only type of cell reproduction in single-celled organisms, so it is very important.

3. For a successful cell division, the cells must contain the correct amount of paired chromosomes with the genetic information, DNA.

4. The genetic information is the same in the different types of cells, unless it is an egg or sperm cell because it only has half.

5. First, asexual reproduction in plants consumes less energy.  Second, asexual reproduction allows all of the genetic information to be passed down to its offspring.

6. In mitosis the DNA must be duplicated so each daughter cell receives a complete set.  In the process of meiosis, the DNA must be duplicated so after two cell divisions there is half set of chromosomes.

7. In interphase the chromosomes are replicated and condensed, in the metaphase step the chromosomes line up at the metaphase plate in the center, in anaphase the chromosomes are pulled apart to the polls, and and during telephase they reach the poles of the cell.

8. The cell cycle is controlled by regulatory proteins.  If control were defective then the cells would continuously divide or die.

#3 Controlling Cell Division:

Cell division is tightly controlled by complexes made of several specific proteins. These complexes contain enzymes called CDKs, turn on or off the various processes that take place in cell division. One such complex is MPF, contains cyclin A or B and cyclin-dependent kinase (CDK). CDK is activated when it is bound to cyclin, interacting with various other proteins that, in this case, allow the cell to proceed from G2 into mitosis. The levels of cyclin change during the cell cycle.

#4 Division of eukaryotic cells to produce genetically identical cells:

1. The first stage of interphase is G1 where the cell grows and functions normally.

2. Next is synthesis which the cell duplicates it's DNA.

3. G2 is the phase in which the cell resumes it's growth and preparation for division.

4. First up in mitosis is condensing the chromatin into chromosomes. The DNA lights up along a central axis and the centrioles send out special tubules to connect to the DNA. Chromatin has now condensed into chromosomes. 2 strands of a chromosome are connected at the center with a centromere. Now chromosomes break at the centromere and the sister chromatids are pulled to the opposite ends of the cell. While the chromosomes are pulled to each side of the cell, the spindle fibers push against the poles of the call that stretch it into an oval. The cell forms into two daughter cells. The nuclear membrane reforms the nuclei reappear and chromosomes unwind back it's a chromatin.

#5 Procedure Questions S87:

1. If the cell contains duplicated chromosomes, there would still be the same amount of genetic material inside of the cell.

2. Chromosomes must condense so they could be separated into a equal halves.

3. The sister chromatids are separated from each other by the spindle fibers.

4. If the sister chromatids did not separate, one daughter cell would be missing a chromosome and the other daughter cell would have two copies of the chromosomes. This situation would end up with both daughter cells dying.

5. If there is lectin protein present, then the process of mitosis will be disrupted in the cell. If there is lectin protein present in the cell, it will have no effects on the process of mitosis. These two hypotheses are not the same,

6. We would use onion bulbs to see the result of its cells after it's been exposed to a solution that has the same effects as lectins. Then we would take a microscope and examine the bulb's cells and notes any significant changes.

7. We would measure the change in size of the cells with a microscope.

8. An appropriate control would be to have an onion bulb that is not exposed to the solution in which the other bulbs are testing.


#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.

Effects of Environment on Mitosis:

1. Place and onion root tip in 6M HCl for 4 minutes

2. Cute off a thin layer and place it on a slide

3. Cover the tip with stain and cover with a cover slip

4. Observe the cells in a microscope and compare it to the control group cells

#7 and #8 Class Data: Observed Values, Expected Values, and Chi-Squared calculations

#9 Critical Values and Null Hypothesis:

If the calculated chi-squared value is great than or equal to the critical value, then the null hypothesis is rejected. If the calculated chi-square value is less than the critical value, then the null hypothesis is not rejected. .

#10 Null Hypothesis:

The chi-squared value is less then our critical value, so the null hypothesis is not rejected (accepted). This means that what is being measured has no effect.

#11 Postlab Review Questions pg S90:

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

Class gives more accurate observed data because of the different trails done.

2. Was there a significant difference between the groups?

Yes there was.

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

No it decreased the number of cells in mitosis.

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

You could repeating the experiment in other plants, to see the different amounts of cells produced by mitosis.

5. Does an increased number of cells in mitosis mean that these cells are dividing faster?


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

You could also measure the mass of the roots over time.


#12 Case 2 Activity pg S92:

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

If a normal cell's DNA has mutation there will be a change in the organism's appearance.  There are different types of mutations, which include point mutation an frame shift. In serious cases this could lead to Down's Syndrome and other disorders.  

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

If the mutated DNA is replicated, other genetic mistakes can occur at a higher rate in the gametes.  It can also cause the deformities to be more extreme, for example can cause the DNA repair enzymes to become mutated.  

3. How do cells monitor DNA integrity?

In cells there are several checkpoint mechanisms monitoring proper regulations of DNA replication.  Certain enzymes also check for single or double strand breaks.

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

5. How do these differences lead to cancer?

Cancerous cells develop from abnormal properties in normal cells that enable them to reproduce uncontrollable and spread. It can be caused by mutations or replication errors. The changes influence cell growth, cell division, and cell aging.

#13 Nondisjunction:

The process where chromosomes do not separate properly and results in gametes with either too many or too few chromosomes.


#14 Different Models of Mitosis and Meiosis:

#15 Pg S93 Questions:

1. When is DNA replicated during meiosis?

DNA is replicated during the S phase of interphase.

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

Homologous chromosomes are similar, but not identical.

3. What is crossing over?

Crossing over is the the exchange of genetic material between homologous chromosomes that results in recombinant chromosomes.

4. What physical constraints control crossover frequencies?

The locus on the chromosomes.

5. What is meant by independent assortment?

When chromatids split apart, they can go in either gamete which allows for more genetic variation.

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

You can multiply all of the independently assorted possibilities.

7. What happens if a homologous pair of chromosomes fails to separate, and how might this contribute to Down's Syndrome?

The cell has a duplicate and one cell has none. Down's Syndrome is also known as Trisomy 21, which is an extra chromosome 21.

8. How are mitosis and meiosis fundamentally different?

Mitosis produces two identical daughter cells, is asexual reproduction, somatic cells undergo this process, diploid cells are produced, and there is one nuclear division. Meiosis produces four sex cells, is sexual reproduction, germ cells undergo this process, haploid cells are produced, and there are two nuclear divisions.

#16 Lab Bench Activity:

#17 Evaluating Results Pg S96:

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

Only half are the result of the crossover.

2. The published map distance is 26 map units. How did the class data compare with this distance?

Our map distance was 31 units. This is a large difference because only 10 items were used in the test pool.

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

Student error or there wasn't enough data points being tested.

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

Crossing over provides genetically different cells.

5. Do you think the Philadelphia chromosome is a result of crossing over?

No, it’s a result of a failed crossing over attempt.

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

No. Although the steps in each process are similar, they result in very different types of cells which have different functions.

#18 Explain Everything:

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