Name
Western Governors University
D312 Anatomy and Physiology I with Lab
Prof. Name
Date
Chromosomes are composed of a complex of DNA and specialized proteins collectively referred to as chromatin. The primary proteins involved are histones, which act as structural scaffolds that allow long DNA molecules to coil tightly and fit within the nucleus. This organization not only ensures efficient packaging of genetic material but also plays a critical role in regulating gene expression, DNA replication, and repair. Genes, which are functional units of heredity, are arranged linearly along these chromosomal DNA strands.
Mitosis and meiosis are both essential processes of cell division in eukaryotic organisms; however, they serve distinct biological purposes and differ significantly in outcomes.
Mitosis is responsible for growth, tissue repair, and cellular maintenance by producing genetically identical daughter cells. Meiosis, on the other hand, is specialized for sexual reproduction and generates genetically diverse gametes.
| Aspect | Mitosis | Meiosis |
|---|---|---|
| Type of parent cell | Diploid | Diploid |
| DNA replication | Occurs once prior to division | Occurs once prior to division |
| Number of divisions | One | Two (Meiosis I and II) |
| Daughter cells produced | Two | Four |
| Genetic makeup of daughter cells | Genetically identical | Genetically distinct |
| Chromosome number | Diploid (46) | Haploid (23) |
| Location | Somatic (body) cells | Germ-line cells |
| Biological purpose | Growth and repair | Sexual reproduction |
Overall, mitosis ensures cellular continuity, while meiosis introduces genetic variation that is essential for evolution and species survival.
Cancer is fundamentally a disease of dysregulated cell division. Under normal circumstances, the cell cycle is tightly regulated by checkpoints and regulatory proteins. When these controls fail, cells may divide uncontrollably.
Two major contributors to cancer development include gene mutations and inherited genetic susceptibility. Mutations in oncogenes or tumor suppressor genes can lead to excessive cell proliferation by bypassing normal regulatory mechanisms. Inherited mutations increase an individual’s predisposition to cancer by weakening cell cycle control from birth.
Based on these mechanisms, potential therapeutic strategies include designing drugs that inhibit DNA replication enzymes specific to cancer cells and developing immunotherapies that enhance the body’s ability to detect and destroy abnormal cells.
It was predicted that interphase would occupy the majority of the cell cycle, lasting approximately 22 hours, while mitosis itself would take about 2 hours.
This prediction is supported by established biological evidence indicating that interphase includes extensive growth, DNA replication, and metabolic activity. In onion root tip cells, which have a roughly 24-hour cell cycle, most cells are expected to be observed in interphase at any given time.
| Phase | Predicted Duration | Explanation |
|---|---|---|
| Interphase | Up to 22 hours | Longest phase involving growth and DNA synthesis |
| Mitosis | ~2 hours | Active division of nucleus |
| Stage | Number of Cells | Total Cells | Percentage of Time |
|---|---|---|---|
| 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% |
The distribution of cells across stages reflects the relative time spent in each phase, confirming that interphase is the most prolonged stage of the cell cycle.
Distinct stages of mitosis—including interphase, prophase, metaphase, anaphase, telophase, and cytokinesis—were observed simultaneously in onion root tip samples. This illustrates that cell division within a tissue is asynchronous, with cells entering different phases independently.
The labeled stages on the slide correspond to the following:
A: Interphase
B: Cytokinesis
C: Prophase
D: Interphase
E: Prophase
F: Metaphase
Most onion root tip cells were observed in interphase. This is expected because interphase encompasses the longest portion of the cell cycle, during which cells grow and prepare for division.
As a cell increases in size, its volume expands more rapidly than its surface area. This decreasing surface area-to-volume ratio limits the efficiency of nutrient intake and waste removal. Cell division restores a favorable ratio, ensuring cellular efficiency and survival.
Mitosis produces new, genetically identical cells that replace damaged or aging cells, supporting growth, tissue maintenance, and repair.
Unregulated mitosis leads to excessive cell accumulation, which can form tumors and ultimately result in cancer.
The predictions were largely accurate, as the majority of cells were observed in interphase, confirming it as the longest phase.
The simultaneous presence of cells in multiple mitotic stages highlighted the continuous and dynamic nature of cell division in growing tissues.
| Question | Answer |
|---|---|
| Chromosome number before mitosis | 46 |
| Chromosome number after mitosis | 46 per daughter cell |
| Example of cells undergoing mitosis | Somatic cells |
| Importance of mitosis | Maintains genetic consistency and tissue integrity |
| Why skin cells divide faster than neurons | Skin cells require frequent renewal; neurons are highly specialized |
| Result of unequal chromatid separation | Aneuploidy and genetic abnormalities |
| Question | Answer |
|---|---|
| Effect of crossing over | Produces genetically unique gametes |
| Ploidy after meiosis I | Haploid |
| Ploidy after meiosis II | Haploid |
| Difference between meiosis I and II | Separation of homologs vs. sister chromatids |
| Severity of nondisjunction | More severe in meiosis I |
| Purpose of chromosome reduction | Maintains stable chromosome number after fertilization |
| Blue whale chromosome count | Gametes: 22; somatic cells: 44 |
| Condition | Description |
|---|---|
| Turner Syndrome (XO) | Missing one sex chromosome |
| Klinefelter Syndrome (XXY) | Extra X chromosome |
| Angelman Syndrome | Chromosomal deletion |
| HeLa Cells | Immortalized cancer cell line |
| Triple X Syndrome (XXX) | Extra X chromosome |
Cancer cells are expected to appear asymmetrical due to disrupted cell cycle regulation. Loss of checkpoint control can result in hereditary and non-hereditary disorders. Somatic mutations that cause cancer are not inherited because they do not affect germ cells.
Cells lacking proper cycle regulation often display abnormal karyotypes due to nondisjunction events. HeLa cells are extensively used in research because of their ability to divide indefinitely, making them valuable for studying cancer and cell cycle mechanisms.
The p53 protein acts as a critical tumor suppressor by regulating DNA repair, metabolism, and apoptosis. When p53 function is compromised, damaged cells may continue dividing, promoting cancer progression.
The Philadelphia chromosome, formed by a translocation between chromosomes 9 and 22, generates an abnormal tyrosine kinase that drives uncontrolled cell proliferation and is strongly associated with chronic myeloid leukemia.
Alberts, B., Johnson, A., Lewis, J., Morgan, D., Raff, M., Roberts, K., & Walter, P. (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., Krieger, M., Bretscher, A., Ploegh, H., Amon, A., & Martin, K. C. (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.
