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 

D312 Anatomy and Physiology I with Lab

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Date

Lab 3: Mitosis and Meiosis BIO201L – Pre-Lab and Post-Lab Analysis

This document presents a restructured, paraphrased, and expanded version of the Lab 3 content on mitosis, meiosis, and cell cycle regulation. The material is organized into clear paragraphs and tables, written in original language to avoid plagiarism, while maintaining APA-style references and academic rigor. Additional explanatory content has been incorporated to strengthen conceptual understanding.

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Pre-Lab Questions

What are chromosomes made of?

Chromosomes are composed of a complex known as chromatin, which consists of DNA tightly associated with histone and non-histone proteins. These proteins provide structural support and enable the efficient packaging of long DNA molecules within the nucleus. Beyond structural organization, chromatin plays a critical regulatory role by controlling gene accessibility, thereby influencing transcription, replication, and DNA repair processes.

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How do mitosis and meiosis compare and contrast?

Mitosis and meiosis are both forms of eukaryotic cell division; however, they differ substantially in purpose, outcome, and genetic consequences. Mitosis supports organismal growth, tissue repair, and cellular maintenance, whereas meiosis is specialized for sexual reproduction and genetic variation.

Comparative Overview of Mitosis and Meiosis

Aspect	Mitosis	Meiosis
Starting cell type	Diploid somatic cell	Diploid germ-line cell
DNA replication	Occurs once before division	Occurs once before meiosis I
Number of divisions	One	Two (meiosis I and meiosis II)
Number of daughter cells	Two	Four
Genetic makeup of daughter cells	Genetically identical	Genetically unique
Chromosome number	Diploid (2n)	Haploid (n)
Primary function	Growth and repair	Sexual reproduction

Mitosis yields two genetically identical diploid daughter cells, preserving chromosome number and genetic stability. In contrast, meiosis produces four haploid cells that differ genetically due to crossing over and independent assortment, processes essential for biological diversity.

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Cancer and Uncontrolled Cell Division: Causes and Potential Drug Development

Cancer is fundamentally a disease of dysregulated cell division. It develops when cells bypass normal cell cycle checkpoints and proliferate uncontrollably. Two primary contributing factors include acquired genetic mutations and inherited predispositions.

Gene mutations can activate oncogenes or inactivate tumor suppressor genes, allowing cells to divide without regulatory constraints. Additionally, individuals may inherit defective genes that increase their susceptibility to cancer development.

Based on these mechanisms, therapeutic strategies may include:

• Designing drugs that inhibit DNA replication enzymes or mitotic spindle formation in rapidly dividing cancer cells.

• Enhancing immune surveillance to improve recognition and destruction of abnormal cells.

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Experiment 1: Observation of Mitosis in a Plant Cell

Mitosis Predictions

It was predicted that interphase would occupy the majority of the cell cycle, lasting approximately 18–22 hours, while mitosis itself would be relatively brief, lasting around 2 hours.

This prediction aligns with established biological knowledge, as cells spend most of their time growing, replicating DNA, and preparing for division rather than actively dividing.

Table 1. Predicted Duration of Cell Cycle Phases

Phase	Predicted Duration	Description
Interphase	Up to 22 hours	Growth, DNA replication, and preparation
Mitosis	~2 hours	Nuclear division

Table 2. Observed Mitosis Data from Onion Root Tip Cells

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%

These percentages reflect the relative duration of each stage, with interphase clearly dominating the cell cycle.

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Observations of Cell Cycle Stages

Distinct stages of the cell cycle were observed microscopically, including interphase, prophase, metaphase, anaphase, telophase, and cytokinesis. Observing these stages simultaneously emphasized that cells within a tissue do not divide synchronously.

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Post-Lab Questions – Experiment 1

Labeling of Cell Cycle Stages

The slide image arrows corresponded to the following stages:

• A: Interphase

• B: Cytokinesis

• C: Prophase

• D: Interphase

• E: Prophase

• F: Metaphase

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

Most cells were observed in interphase. This finding is expected because interphase encompasses cell growth, DNA replication, and metabolic activity, making it the longest phase of the cell cycle.

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How does the surface area-to-volume ratio relate to cell division?

As a cell increases in size, its volume grows more rapidly than its surface area. This decrease in surface area-to-volume ratio limits the efficiency of nutrient uptake and waste removal. Cell division restores a favorable ratio, allowing cells to maintain homeostasis.

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What is the function of mitosis in dividing cells?

Mitosis ensures that each daughter cell receives an identical set of chromosomes, enabling growth, tissue repair, and replacement of damaged or aging cells while preserving genetic consistency.

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What are the consequences of uncontrolled mitosis?

When mitosis occurs without regulatory control, cells proliferate excessively, forming tumors and potentially leading to cancer due to the accumulation of abnormal cells.

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Accuracy of time predictions

The predictions regarding stage duration were largely accurate, as interphase accounted for the highest proportion of observed cells, confirming it as the longest phase.

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Notable observations from onion root tip cells

A key observation was the presence of multiple mitotic stages within the same tissue sample, illustrating the continuous and asynchronous nature of cell division in growing plant roots.

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Experiment 2: Tracking Chromosomes Through Mitosis

Post-Lab Analysis

Question	Answer
Chromosome number before mitosis	46 chromosomes
Chromosome number after mitosis	46 chromosomes per daughter cell
Example of cells undergoing mitosis	Somatic cells, ensuring tissue integrity
Reason skin cells divide faster than neurons	Continuous renewal vs. specialization
Effect of unequal chromatid separation	Genetic imbalance and potential disorders

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Experiment 3: Tracking Chromosomal DNA Movement Through Meiosis

Post-Lab Analysis

Question	Answer
Role of crossing over	Creates genetic variation in gametes
Ploidy after meiosis I	Haploid
Ploidy after meiosis II	Haploid (four cells)
Difference between meiosis I and II	Homologs vs. sister chromatids
Severity of nondisjunction	More severe in meiosis I
Purpose of chromosome reduction	Maintain species chromosome number
Chromosome count in blue whales	Gametes: 22; mitosis: 44

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Experiment 4: The Importance of Cell Cycle Control

Examples of Chromosomal Abnormalities

Condition	Description
Turner Syndrome (XO)	Missing one X chromosome
Klinefelter Syndrome (XXY)	Extra X chromosome
Angelman Syndrome	Chromosomal deletion
Triple X Syndrome (XXX)	Extra X chromosome
HeLa Cells	Immortal cancer cell line

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Post-Lab Discussion

Cancer cells are predicted to display abnormal shapes and division patterns due to defective cell cycle checkpoints. Disruption of cell cycle regulation contributes to both inherited and acquired diseases.

Somatic mutations that cause cancer are not passed to offspring because they do not affect germ cells. Cells lacking cycle control often exhibit abnormal karyotypes due to nondisjunction events.

HeLa cells are extensively used in research because of their unlimited division capacity, making them valuable for studying cancer biology and therapeutic development.

The p53 protein functions as a critical tumor suppressor by regulating DNA repair, cell cycle arrest, and apoptosis. Mutations in p53 compromise genome stability and promote cancer progression.

The Philadelphia chromosome results from a translocation between chromosomes 9 and 22, creating an abnormal tyrosine kinase that drives uncontrolled cell division, particularly in chronic myeloid leukemia.

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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.

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

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.