D312 Lab 3: Mitosis, Meiosis, and Cancer – Pre/Post Lab Insights
Student Name
Western Governors University
D312 Anatomy and Physiology I with Lab
Prof. Name
Date
Lab 3 Mitosis and Meiosis BIO201L Pre-Lab Questions
1. What are chromosomes made of?
Chromosomes consist of protein complexes known as chromatin, which organize DNA into specific units called genes. This chromatin-DNA structure allows the compact packaging of genetic material while enabling gene regulation and expression.
2. Compare and contrast mitosis and meiosis.
| Aspect | Mitosis | Meiosis |
|---|---|---|
| Starting cell type | Begins with diploid parent cells | Begins with diploid parent cells |
| DNA replication | DNA is copied once before division | DNA is copied once before division |
| Type of division | Cell division in eukaryotic cells | Cell division in eukaryotic cells |
| Number of daughter cells | Produces two daughter cells identical to parent | Produces four daughter cells genetically different from each other |
| Location | Occurs throughout the body (somatic cells) | Occurs only during sexual reproduction (gametes) |
| Chromosome number in daughters | Daughter cells have 46 chromosomes (diploid) | Daughter cells have 23 chromosomes (haploid) |
Mitosis produces two genetically identical diploid daughter cells, suitable for growth and repair. Meiosis, in contrast, produces four genetically diverse haploid cells essential for sexual reproduction, involving two rounds of cell division.
3. Cancer and Uncontrolled Cell Division: Causes and Potential Drug Development
Cancer arises from uncontrolled cell division. Two major causes include:
- Gene Mutations: Mutations accelerate cancer cell division by increasing growth factors and bypassing normal cell cycle regulation.
- Inherited Cancer: Genetic predisposition causes susceptibility to rapid and unregulated cell growth.
Based on these insights, an effective drug could be designed to:
- Inhibit the replication machinery of cancer cells, thereby slowing or stopping their division.
- Enhance immune system function to target and eliminate cancer cells more efficiently.
Experiment 1: Observation of Mitosis in a Plant Cell
Mitosis Predictions
Prediction:
Interphase will take up to 22 hours, being the longest phase in the cell cycle, while mitosis will last approximately 2 hours.
Supporting Evidence:
Interphase typically dominates the cell cycle, lasting about 18-24 hours. The onion root tip cells studied have a cycle of about 24 hours, with interphase expected to occupy the majority of this time.
Table 1: Mitosis Predictions
| Phase | Predicted Duration | Notes |
|---|---|---|
| Interphase | Up to 22 hours | Longest phase, most time spent here |
| Mitosis | Approximately 2 hours | Cell division phase |
Table 2: Mitosis Data 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: The percentage reflects the relative time the cells spend in each stage.
Observations on Cell Stages (with drawings as part of the experiment)
- Interphase
- Prophase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
Post-Lab Questions
1. Label the arrows on the slide image with the appropriate cell cycle stages.
- A: Interphase
- B: Cytokinesis
- C: Prophase
- D: Interphase
- E: Prophase
- F: Metaphase
2. In which stage were most onion root tip cells found? Why?
Most cells were in interphase, which aligns with the understanding that this phase is the longest in the cell cycle, allowing the cell to grow and prepare for division.
3. How does the surface area to volume ratio change as a cell grows, and how is this related to cell division?
As a cell grows, its surface area to volume ratio decreases. For example, blowing up a balloon increases the volume faster than the surface area. A decreasing ratio limits efficient diffusion of nutrients and waste, signaling the need for cell division to restore a favorable ratio.
4. What is the function of mitosis in a cell about to divide?
Mitosis replaces old, damaged, or worn-out cells by producing new cells that are genetically identical to the parent, ensuring proper growth and maintenance.
5. What would be the consequence of uncontrolled mitosis?
Unregulated mitosis leads to excessive cell proliferation, potentially resulting in cancer as abnormal cells continuously divide and accumulate.
6. How accurate were your time predictions for each cell cycle stage?
Predictions were fairly accurate; most cells were in interphase, supporting the notion that it is the longest phase.
7. What interesting observation did you make while examining the onion root tip cells?
It was interesting to observe mitosis occurring in various stages simultaneously, highlighting the dynamic nature of cell division during growth.
Experiment 2: Tracking Chromosomes Through Mitosis
Post-Lab Questions
| Question | Answer |
|---|---|
| How many chromosomes were present before mitosis? | 46 chromosomes |
| How many chromosomes did daughter cells contain after mitosis? | 46 chromosomes per daughter cell |
| Example of a cell that undergoes mitosis and importance? | Eukaryotic somatic cells. Identical information ensures proper cell function and tissue integrity. |
| Why do skin cells divide faster than neurons? | Skin cells protect the body and require frequent renewal; neurons are more specialized and divide less. |
| What happens if sister chromatids fail to split equally? | Unequal distribution causes one cell to have excess chromosomes and the other to be deficient, leading to genetic abnormalities. |
Experiment 3: Tracking Chromosomal DNA Movement Through Meiosis
Post-Lab Questions
| Question | Answer |
|---|---|
| How does crossing over affect genetic content in gametes? | Crossing over exchanges chromosome segments, generating unique genetic combinations in gametes, enhancing genetic diversity. |
| What is the ploidy after meiosis I and meiosis II? | Meiosis I produces haploid daughter cells; meiosis II maintains haploid status but results in four cells. |
| Differences between meiosis I and meiosis II | Meiosis I separates homologous chromosomes and involves crossing over; meiosis II separates sister chromatids and does not involve crossing over. |
| Severity of nondisjunction in meiosis I vs. meiosis II | Nondisjunction in meiosis I affects homologous chromosomes and is generally more severe, leading to disorders like Down Syndrome. |
| Why reduce chromosome number in gametes but not in other cells? | Gametes must be haploid to ensure chromosome number remains stable after fertilization; somatic cells remain diploid for normal function. |
| Chromosome count in blue whale cells | Sperm and egg cells: 22 chromosomes each; daughter cells from mitosis: 44 chromosomes; daughter cells from meiosis II: 22 chromosomes. |
Experiment 4: The Importance of Cell Cycle Control
Examples of Chromosomal Abnormalities
| Syndrome | Description |
|---|---|
| Turner’s Syndrome (XO) | Missing sex chromosome |
| Klinefelter Syndrome (XXY) | Extra sex chromosome |
| Angelman Syndrome | Chromosomal deletion |
| HeLa Cells | Immortalized cancer cell line |
| Triple X Syndrome (XXX) | Extra sex chromosome |
Post-Lab Questions
- Hypothesis:
Cancer cells will appear asymmetrical compared to normal cells undergoing typical cell cycles. - Cell cycle control results:
Disruption in cell cycle control leads to hereditary and non-hereditary diseases; lack of control results in severe health consequences. - Inheritance of somatic mutation causing cancer:
Cancer-causing mutations in somatic cells are generally not inherited by offspring because they do not affect germ cells responsible for passing on genetic material. - Why do cells lacking cycle control show abnormal karyotypes?
Loss of cell cycle checkpoints causes nondisjunction during meiosis, resulting in abnormal chromosome numbers and structures in daughter cells. - HeLa cells and their experimental use:
HeLa cells are immortal cancerous epithelial cells widely used in research due to their ability to continuously divide and their relevance in studying cell cycle and cancer. - Function of p53 protein:
p53 regulates hundreds of genes involved in DNA repair and metabolic adaptation; it can induce cell cycle arrest or apoptosis, maintaining genome integrity but its malfunction can lead to cancer progression. - Philadelphia chromosome and cancer:
This abnormal chromosome results from translocation between chromosomes 9 and 22, producing an abnormal tyrosine kinase enzyme that promotes cancer cell proliferation, commonly seen in chronic myeloid leukemia (CML).
References
Weinberg, R. A. (2014). The Biology of Cancer (2nd ed.). Garland Science.
Alberts, B., Johnson, A., Lewis, J., et al. (2015). Molecular Biology of the Cell (6th ed.). Garland Science.
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
D312 Lab 3: Mitosis, Meiosis, and Cancer – Pre/Post Lab Insights
Cooper, G. M. (2000). The Cell: A Molecular Approach (2nd ed.). Sinauer Associates.