Lab 7 - Cell Division: Mitosis and Meiosis #NPAPBio

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

Pre-Lab Questions

1. How did you develop from a single-celled zygote to an organism with trillions of cells?

My cells simply underwent mitosis many times. As the cells continued to reproduce through mitosis, the number of total cells began to exponentially grow until millions upon millions of cells are formed.

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

Cell division allows the organism to asexually reproduce. Without cell division, single-celled organism would lose the ability to reproduce and produce more organisms.

3. What must happen to ensure successful cell division?

DNA must be duplicated successfully, and the number of DNA in the new cell must equate to the DNA of the mother cell. The process of mitosis must also be successful, meaning that all steps of mitosis are carried through completion.

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

They are identical.

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

No partner is needed for reproduction. Genetic code does not vary between generations.

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

The amount of DNA must be constant from generation to generation.

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

Mitotic spindle fibers guide them.

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

A checkpoint system controls the cycle. Defective control may allow rampant cell division.

Cell division involves the distribution of identical genetic material, DNA, to two daughters cells. Mitosis is a fundamental process for life. During mitosis, a cell duplicates all of its contents, including its chromosomes, and splits to form two identical daughter cells. Because this process is so critical, the steps of mitosis are carefully controlled by a number of genes.


Every time a Eukaryotic cell divides to produce two new daughter cells, all the DNA molecules of the parent cell are fully copied and combined with histones to form compact packages. In the process called mitosis, one complete set of chromosomes is transmitted to each new daughter cell. This process ensures that each offspring is genetically identical to the parent cell.

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, the daughter cell does not contain any more information than the mother cell. The genetic material is duplicated then split, meaning that the daughter cells have the same amount of genetic information.

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

Chromosomes condense before mitosis to allow them the ability to move smoothly, without becoming entangled and breaking.

How are the chromosomes copied, called sister chromatids, separated from each other?

During anaphase, each pair of chromosomes is separated into two identical, independent chromosomes. The chromosomes are separated by a structure called the mitotic spindle.

What would happen if sister chromatid failed to separate?

If sister chromatids were not separated during mitosis, the daughter cells would not have an exact copy of the parent cell's chromosomes. One daughter cell would be missing a chromosome and the other daughter cell would have two copies of one chromosome. The most likely situation is that both daughter cells would die.


“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.

Experiment Design:

To observe the effect of a lectin-like protein on the growth of root apical meristem tissue, we put both lectin treated and lectin-free controlled onion roots under a microscope.  The next step was counting the cells and categorizing them as "Interphase" or "Mitotic." Interphase cells could be seen as an empty cell or a compact black dot. Mitotic cells were any of the cells that looked similar to the steps of mitosis. For example, if we observed distinct bundling of chromosomes or distinct splitting of chromosomes, we would conclude the cell was undergoing mitosis. After counting the "type" of cells, the class compiled the data together. Comparing these results to the expected data would allow us to determine whether the null hypothesis was valid or not.

Null Hypothesis: Treating onion roots in a lectin solution will not increase the rate of mitosis in cells, but rather the rate at which mitosis occurs will decrease due to the lectin treatment.

Data Table Showing Untreated and Treated Cells

Table of Observed/Expected Values:

Chi-Squared Value Table:

The Degree of Freedom is 1 (Number of Treatemnet Groups minus one)X(Number of phase groups minus one).

The Probability is given as 0.05.

Meaning that if our Chi-Squared value is is less than 3.84, then our null hypothesis is not ignored.

0.9713 < 3.84

The null hypothesis is accepted, not rejected. This means that our hypothesis was correct.


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

If there is a mutation in DNA, then the organism may have deformities or disorders. If a base in the DNA sequence is deleted, inserted, or changed in any way, there is a chance that the codon may change itself, thus coding for a different proteins.

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

The replication of mutated DNA would have huge implications on the functionality and survival of the daughter cells. One primary example of a fatal result is cancer. As the mutated DNA continues to replicate, the condition only progresses throughout the cells.

3. How do cells monitor DNA integrity?

Obviously if DNA cannot sustain cell life, mutated cells die. If the implication does not kill the cell, cells may undergo apoptosis to maintain DNA integrity throughout the entire organism.

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

Cancer cells no longer function in a normal way. Normal cells have switching signals and checks and balances that tell them when to die so that other cells can live. In a cancer cell this signaling system has been cut off. Mutation(s) in the genes that govern the cell cause this system to be changed, so that either the cell is instructed by the gene to keep replicating, or the normal stop signal that would tell it when to stop replicating has been removed.

5. How could these differences lead to cancer?

Every cell that divides from the original faulty cancer cell also has the same faulty code, and eventually there are enough of these faulty cells to form a tumor. The cancerous cells continue to replicate without end.

Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate evenly and properly during mitosis or meiosis. Most commonly, Trisomy 21 is an example of nondisjunction. Nondisjunction can lead to major cell implications that can effect the entire cell, or even the entire organism as in Trisomy 21.


-The DNA is replicated during the Interphase of meiosis. This is during the Meiosis I phase of meiosis. This process is identical to the DNA replication in mitosis.

-No, one homologous chromosome comes from the mother and one from the father. The chromosomes code for the identical genes, but the nitrogenous bases are arranged differently. In addition, crossing-over occurs, meaning the chromosomes are genetically varied.

-Crossing-over is when a small fragment of DNA is broken off of one homologous chromosome and transfers into the homologous chromosome during meiosis.

-The distance between the gene and the centromere of each chromosome controls crossover frequencies. For example if a specific gene is very close to the centromere, it is less likely that the gene will crossover. Genes further away from the centromere and closer to the end of the  chromosome will be more likely to cross over to the other homologous chromosome.

-alleles for a trait separate when meiosis occurs. This occurs independently of other alleles, thus making gametes genetically unique. During fertilization, these alleles join randomly creating very varied cellular DNA.

-Take 2 and raise it to the power of n where n=# of heterozygous gene pairs.

For example, if we have 3 gene pairs we raise 2^3 and find that there would be 8 gamete possibilities.

-If homologous chromosomes fail to separate, no disjunction may occur. This means one sex cell will have too many genes and another will have too little. This may lead to cell implications such as Trisomy 21. As a result, Down syndrome occurs in humans. Another example of the effects of no disjunction is cri du chat. This occurs when a piece of chromosome 5 goes missing during meiosis.

-Mitosis produces two identical daughter cells with a 2n number of chromosomes. This means the daughter cells have the same number of genes as a normal cell, the diploid number. Meiosis has two phases, in which DNA is separated twice. This means the resulting 4 daughter cells have half the number of chromosomes. The daughter cells are known as sex cells, designed to undergo fertilization; these cells are haploid.


1. We divided the percent of crossovers by two because each crossover produces two spores like the parents. So, the number of asci we count is actually double the number of crossovers. To find the number of crossovers, we must work backwards by dividing by 2. This number is the correct number of crossovers.

2. The class data was 31.8. This means the experiment the class ran had a significant higher amount of crossing overs more than the published map

3. A possible explanation for the disparity between the class data and the published data is that the population size of the tested spores was very small. Considering that the class tested the same 10 spores, the chances of outliers are very high. Any outlier could be the reason why the results were so different.

4. During meiosis, crossing over occurs. This results in the spores either being extremely varied or being simple. Spores that undergo crossing-over experience variety.

5. The Philadeplhia chromosome is the result of a mistake in crossing over. I can conclude this because one chromosome has too many genes and the other has too little. This leads me to believe that when the genes crossed over, the broken genes did not find their way to the other homologous chromosome.

6. No, the cell cycles of mitosis and meiosis are unique. In mitosis, the genes are separated once. In meiosis, the genes undergo splitting twice. Also, in meiosis, crossing-over occurs. This process is not seen in mitosis.

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