D312 Lab 3: Mitosis, Meiosis, and Cancer – Pre/Post Lab Insights

D312 Lab 3: Mitosis, Meiosis, and Cancer – Pre/Post Lab Insights

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 Western Governors University

D269 Composition: Writing with a Strategy

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Lab 3: Mitosis and Meiosis

BIO201L Pre-Lab Questions

1. What Are Chromosomes Made Of?

Chromosomes are structures composed of DNA tightly packed with proteins called chromatin. This complex organization allows the long DNA molecules to be efficiently condensed into compact units. Chromatin not only provides structural support but also plays a crucial role in regulating gene expression by controlling which genes are accessible for transcription. Through this arrangement, chromosomes maintain the integrity and functionality of genetic information within cells.

2. Compare and Contrast Mitosis and Meiosis

Mitosis and meiosis are two forms of cell division with distinct purposes and outcomes.

Aspect	Mitosis	Meiosis
Starting Cell Type	Diploid parent cells	Diploid parent cells
DNA Replication	DNA replicates once before division	DNA replicates once before division
Type of Division	Occurs in somatic (body) cells	Occurs only in germ cells (sexual reproduction)
Number of Daughter Cells	Two genetically identical diploid cells	Four genetically diverse haploid cells
Chromosome Number in Daughters	Daughter cells maintain 46 chromosomes (diploid)	Daughter cells have 23 chromosomes (haploid)
Biological Role	Growth, repair, and maintenance	Production of gametes for sexual reproduction

Mitosis ensures tissue growth and repair by producing two identical daughter cells, maintaining chromosome number. Meiosis, on the other hand, reduces chromosome number by half, producing genetically unique haploid cells necessary for sexual reproduction, involving two consecutive divisions.

3. Cancer and Uncontrolled Cell Division: Causes and Drug Development Potential

Cancer arises when cell division becomes uncontrolled. This can occur due to:

• Gene Mutations: Changes in genes that increase growth factor production or disable cell cycle checkpoints, leading to unchecked proliferation.
• Inherited Cancer Predisposition: Genetic factors that increase susceptibility to rapid and unregulated cell growth.

Potential drug strategies include:

• Designing inhibitors targeting the replication machinery in cancer cells to slow or halt their division.
• Enhancing the immune response to better identify and destroy malignant cells.

Experiment 1: Observation of Mitosis in a Plant Cell

Mitosis Predictions

It is predicted that interphase will last approximately 22 hours, constituting the longest phase of the cell cycle, while mitosis will span around 2 hours. This prediction is supported by evidence showing that interphase occupies the majority of the cell cycle, particularly in onion root tip cells, which typically complete a cycle in about 24 hours.

Phase	Predicted Duration	Notes
Interphase	Up to 22 hours	Longest phase in the cycle
Mitosis	Approximately 2 hours	Cell division phase

Data Collected from Onion Root Tip Cells

Stage	Number of Cells	Total Cells	% Time Spent in Stage
Interphase	14	34	41.18%
Prophase	4	34	11.76%
Metaphase	5	34	14.71%
Anaphase	6	34	17.65%
Telophase	3	34	8.82%
Cytokinesis	2	34	5.88%

Note: Percentages indicate the relative time cells spend in each mitotic stage.

Observations of Cell Stages

• Interphase: Cells prepare for division by growing and replicating DNA.
• Prophase: Chromosomes condense, spindle fibers form.
• Metaphase: Chromosomes align at the cell center.
• Anaphase: Sister chromatids separate.
• Telophase: Chromosomes decondense, nuclear membranes reform.
• Cytokinesis: Cytoplasm divides, forming two daughter cells.

Post-Lab Questions

1. Label the cell cycle stages shown in the slide image:

Arrow	Cell Cycle Stage
A	Interphase
B	Cytokinesis
C	Prophase
D	Interphase
E	Prophase
F	Metaphase

2. In which stage were most onion root tip cells found, and why?

Most cells were found in interphase, consistent with it being the longest phase, during which cells grow and prepare for division.

3. How does the surface area to volume ratio change as a cell grows, and what is the connection to cell division?

As a cell enlarges, its volume increases faster than its surface area, decreasing the surface area-to-volume ratio. This ratio drop limits efficient nutrient and waste exchange, triggering cell division to restore optimal ratios.

4. What is the role of mitosis in a cell about to divide?

Mitosis produces genetically identical cells that replace damaged or aged cells, supporting growth and tissue maintenance.

5. What could be the consequence of uncontrolled mitosis?

Unregulated mitosis leads to excessive cell proliferation, often resulting in tumor formation and cancer development.

6. How accurate were the predictions regarding the duration of each cell cycle stage?

The predictions were quite accurate, particularly for interphase, confirming it as the longest stage.

7. What interesting observations were made about mitosis in onion root tip cells?

It was intriguing to observe multiple mitotic phases occurring simultaneously, demonstrating the continuous and dynamic process of cell division in growing tissues.

Experiment 2: Tracking Chromosomes Through Mitosis

Question	Answer
How many chromosomes were present before mitosis?	46 chromosomes
How many chromosomes did daughter cells have after mitosis?	46 chromosomes per daughter cell
Example of a cell that undergoes mitosis and its importance	Eukaryotic somatic cells; ensures genetic consistency and tissue function integrity
Why do skin cells divide faster than neurons?	Skin cells require frequent renewal for protection; neurons are highly specialized and divide rarely
What happens if sister chromatids fail to separate equally?	Unequal chromosome distribution causes genetic abnormalities in daughter cells

Experiment 3: Tracking Chromosomal DNA Movement Through Meiosis

Question	Answer
How does crossing over affect genetic content in gametes?	Crossing over exchanges chromosome segments, creating genetically unique gametes and enhancing diversity
What is the ploidy after meiosis I and meiosis II?	Meiosis I produces haploid cells; meiosis II maintains haploidy, resulting in four haploid cells
Differences between meiosis I and meiosis II	Meiosis I separates homologous chromosomes with crossing over; meiosis II separates sister chromatids without crossing over
Severity of nondisjunction in meiosis I vs. meiosis II	Nondisjunction in meiosis I generally causes more severe abnormalities, such as Down Syndrome
Why reduce chromosome number in gametes but not in other cells?	Gametes must be haploid to maintain chromosome number stability after fertilization; somatic cells remain diploid
Chromosome count in blue whale cells	Sperm and egg cells: 22 chromosomes each; mitotic daughter cells: 44 chromosomes; meiotic daughter cells: 22 chromosomes

Experiment 4: The Importance of Cell Cycle Control

Syndrome	Description
Turner’s Syndrome (XO)	Missing one sex chromosome
Klinefelter Syndrome (XXY)	Extra sex chromosome
Angelman Syndrome	Chromosomal deletion
HeLa Cells	Immortal cancerous cell line
Triple X Syndrome (XXX)	Extra sex chromosome

Post-Lab Questions

• Hypothesis: Cancer cells will show asymmetry compared to normal cells due to disrupted cell cycle regulation.
• Results of cell cycle control: Failure to regulate the cell cycle leads to diseases, both inherited and acquired, often with serious health implications.
• Inheritance of somatic mutation causing cancer: Somatic mutations typically are not passed to offspring since they do not occur in germ cells.
• Why do cells lacking cycle control show abnormal karyotypes? Loss of cell cycle checkpoints causes errors like nondisjunction, resulting in cells with abnormal chromosome numbers and structures.
• HeLa cells and their use: HeLa cells are immortalized cancer cells widely used in research to study cell division, cancer mechanisms, and drug responses.
• Function of p53 protein: p53 regulates genes involved in DNA repair, cell cycle arrest, and apoptosis, preserving genome stability. Its malfunction contributes to cancer progression.
• Philadelphia chromosome and cancer: This chromosome arises from a translocation between chromosomes 9 and 22, producing an abnormal tyrosine kinase that drives cancer cell proliferation, notably in chronic myeloid leukemia (CML).

References

Alberts, B., Johnson, A., Lewis, J., et al. (2015). Molecular Biology of the Cell (6th ed.). Garland Science.

Cooper, G. M. (2000). The Cell: A Molecular Approach (2nd ed.). Sinauer Associates.

Lodish, H., Berk, A., Kaiser, C. A., et al. (2020). Molecular Cell Biology (8th ed.). W.H. Freeman.

National Cancer Institute. (n.d.). Cancer and the Cell Cycle. https://www.cancer.gov/about-cancer/understanding/what-is-cancer

Weinberg, R. A. (2014). The Biology of Cancer (2nd ed.). Garland Science.