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

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

Pre-Lab Questions

1. What are chromosomes made of?

Chromosomes consist primarily of deoxyribonucleic acid (DNA) and proteins known as histones, which together form a complex called chromatin. DNA carries the genetic instructions essential for an organism’s growth, development, and reproduction. The histone proteins provide structural support, allowing DNA to coil tightly and fit within the cell nucleus. This organization helps regulate gene expression, replication, and repair, ensuring that genetic information is accurately transmitted during cell division (Alberts et al., 2022).

2. Compare and contrast mitosis and meiosis

Both mitosis and meiosis are forms of eukaryotic cell division, but they serve distinct biological purposes.

Comparison

Aspect	Mitosis	Meiosis
Parent Cell Type	Begins from a diploid parent cell	Begins from a diploid parent cell
DNA Replication	DNA replicates once before division	DNA replicates once before division
Cell Division Type	Occurs in eukaryotic cells	Occurs in eukaryotic cells

Contrast

Aspect	Mitosis	Meiosis
Number of Divisions	One division producing two daughter cells	Two divisions producing four daughter cells
Genetic Identity	Daughter cells are identical to the parent cell	Daughter cells are genetically unique
Occurrence	Occurs in somatic (body) cells	Occurs in germ (sex) cells
Chromosome Number	Produces diploid (2n) cells with 46 chromosomes	Produces haploid (n) cells with 23 chromosomes

Mitosis maintains genetic consistency across body cells, while meiosis promotes genetic diversity through recombination and independent assortment (Griffiths et al., 2020).

3. Cancer and Uncontrolled Cell Division

Cancer arises when normal regulatory mechanisms controlling cell division malfunction. Two major causes include gene mutations and inherited genetic defects. Mutations in genes such as p53 and BRCA1 can disrupt normal cell cycle regulation, leading to unchecked cellular proliferation. Inherited mutations can predispose individuals to various cancers, as they compromise DNA repair and apoptosis mechanisms (Hanahan & Weinberg, 2011).

To inhibit cancer progression, I propose developing a dual-action therapeutic drug. This compound would (1) target and disrupt the replication machinery specific to cancer cells, reducing their ability to divide, and (2) enhance immune function by stimulating cytotoxic T-cells, enabling the body to recognize and eliminate malignant cells. Such an approach would slow tumor growth while improving patient immune resilience.

Experiment 1: Observation of Mitosis in a Plant Cell

Table 1: Mitosis Predictions

Prediction	Explanation
Interphase Duration: 22 hours	Interphase is typically the longest stage of the cell cycle, during which DNA replication and growth occur.
Mitotic Duration: 2 hours	The mitotic phase is shorter, as it involves rapid nuclear and cytoplasmic division.

Supporting Evidence:
In plant cells, especially onion (Allium cepa) root tips, interphase occupies the majority of the cell’s life cycle—approximately 18 to 24 hours. The prediction that interphase lasts around 22 hours aligns with established data showing that mitosis itself is a relatively brief process (Cooper & Hausman, 2020).

Table 2: Mitosis Data (Onion Root Tip)

Stage	Number of Cells in Stage	Total Number of Cells	Percentage of Time Spent in Stage (%)
Interphase	14	34	9.88
Prophase	4	34	2.82
Metaphase	5	34	3.52
Anaphase	6	34	4.23
Telophase	3	34	2.12
Cytokinesis	2	34	1.41

Post-Lab Questions

1. Label the stages of the cell cycle in the provided slide image

A – Interphase
B – Cytokinesis
C – Prophase
D – Interphase
E – Prophase
F – Metaphase

2. What stage were most onion root tip cells in? Why?

The majority of onion root tip cells were observed in interphase. This is expected since interphase represents the longest phase in the cell cycle, encompassing DNA replication and cellular growth before mitosis. Cells spend approximately 90% of their life cycle in interphase (Alberts et al., 2022).

3. Surface Area to Volume Ratio and Cell Division

As a cell increases in size, its surface area-to-volume ratio decreases. This phenomenon limits the efficiency of nutrient uptake and waste removal. To maintain homeostasis, the cell undergoes division, restoring a favorable ratio that enhances diffusion and metabolic exchange (Cooper & Hausman, 2020).

4. Function of Mitosis in a Dividing Cell

The main function of mitosis is to ensure cellular replacement, growth, and tissue repair. Mitosis produces two genetically identical daughter cells, preserving the organism’s chromosomal integrity (Griffiths et al., 2020).

5. Consequences of Uncontrolled Mitosis

If mitosis becomes uncontrolled, cells divide continuously, leading to tumor formation and potential malignancy. This unregulated division is a hallmark of cancer (Hanahan & Weinberg, 2011).

6. Accuracy of Time Predictions

The predicted durations of the mitotic phases were reasonably accurate, as the majority of observed cells were indeed in interphase, validating that this phase dominates the cycle.

7. Interesting Observation

A fascinating aspect of the onion root tip observation was the synchronization of mitotic stages across cells, highlighting the precise regulation of cell division in plant growth zones.

Experiment 2: Tracking Chromosomes Through Mitosis

Post-Lab Questions

1. How many chromosomes were present before mitosis?
   46 chromosomes.

2. How many chromosomes did each daughter cell contain after mitosis?
   Each daughter cell contained 46 chromosomes, identical to the parent cell.

3. Example of a cell type undergoing mitosis and its importance
   Human skin cells undergo mitosis frequently to replace damaged tissue. It is crucial for daughter cells to contain identical genetic material to maintain skin integrity and function.

4. Why do skin cells divide faster than neurons?
   Skin cells experience constant wear and tear and must divide rapidly to repair and renew tissue, whereas neurons are long-lived and rarely divide.

5. What happens if sister chromatids fail to separate equally during anaphase?
   Unequal separation results in aneuploidy, where one daughter cell has extra chromosomes and the other has too few, potentially causing genetic disorders (Cooper & Hausman, 2020).

Experiment 3: Following Chromosomal DNA Movement Through Meiosis

Post-Lab Questions

1. Effect of Crossing Over
   Crossing over promotes genetic variation by exchanging DNA segments between homologous chromosomes, producing unique combinations in gametes.

2. Ploidy of Daughter Cells

   • End of Meiosis I: Two haploid cells

   • End of Meiosis II: Four haploid cells

3. Differences Between Meiosis I and II

Feature	Meiosis I	Meiosis II
Number of Cells Produced	2	4
Chromosome Type	Homologous chromosomes separate	Sister chromatids separate
Crossing Over	Occurs	Does not occur

4. Severity of Nondisjunction
   Nondisjunction in meiosis I is more severe because entire homologous pairs fail to separate, leading to significant chromosomal abnormalities such as Down or Turner Syndrome.

5. Why Reduce Chromosome Number in Gametes
   Gametes must contain half the number of chromosomes (haploid) so that upon fertilization, the resulting zygote restores the diploid number.

6. Chromosome Counts in Blue Whales

Cell Type	Number of Chromosomes
Sperm Cell	22
Egg Cell	22
Daughter Cell (Mitosis)	44
Daughter Cell (Meiosis II)	22

Experiment 4: The Importance of Cell Cycle Control

Data Table

Syndrome/Cell Type	Description	Chromosomal Abnormality
Turner’s Syndrome	Monosomy (X0)	Missing X chromosome
Klinefelter Syndrome	XXY pattern	Extra X chromosome
Angelman Syndrome	Deletion disorder	Missing chromosome fragment
HeLa Cell	Cancerous epithelial cell	Abnormal growth pattern
Triple X Syndrome	XXX	Extra X chromosome

Post-Lab Questions

1. Hypothesis
   Cancer cells are expected to display irregular and asymmetric shapes, unlike normal cells that exhibit uniform morphology.

2. Implications of Cell Cycle Control
   Proper cell cycle regulation prevents uncontrolled growth. When disrupted, cells may develop genetic abnormalities or cancerous behavior.

3. Inheritance of Somatic Mutations
   Somatic mutations, such as those causing cancer, cannot be inherited because they do not affect germ cells. Only germline mutations can be passed to offspring.

4. Appearance of Abnormal Karyotypes
   Cells lacking proper cycle control exhibit distorted or irregular karyotypes due to nondisjunction events during meiosis.

5. What Are HeLa Cells?
   HeLa cells are immortalized human epithelial cancer cells derived in 1951 from Henrietta Lacks. Their unlimited replicative capacity makes them ideal for studying cell division, mutation, and cancer biology.

6. Function of Protein p53
   The p53 protein acts as a tumor suppressor, regulating over 500 genes involved in DNA repair, apoptosis, and cell cycle arrest. When mutated, p53 fails to stop damaged cells from dividing, contributing to cancer development.

7. Philadelphia Chromosome and Cancer
   The Philadelphia chromosome results from a translocation between chromosomes 9 and 22, producing the BCR-ABL fusion gene. This gene encodes an abnormal tyrosine kinase enzyme that drives unregulated cell division, leading to chronic myelogenous leukemia (Rowley, 1973).

References

Alberts, B., Johnson, A., Lewis, J., Morgan, D., Raff, M., Roberts, K., & Walter, P. (2022). Molecular biology of the cell (7th ed.). W. W. Norton & Company.

Cooper, G. M., & Hausman, R. E. (2020). The cell: A molecular approach (8th ed.). Oxford University Press.

Griffiths, A. J. F., Wessler, S. R., Carroll, S. B., & Doebley, J. (2020). Introduction to genetic analysis (12th ed.). W. H. Freeman.

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

Hanahan, D., & Weinberg, R. A. (2011). Hallmarks of cancer: The next generation. Cell, 144(5), 646–674. https://doi.org/10.1016/j.cell.2011.02.013

Rowley, J. D. (1973). A new consistent chromosomal abnormality in chronic myelogenous leukemia identified by quinacrine fluorescence and Giemsa staining. Nature, 243(5405), 290–293. https://doi.org/10.1038/243290a0

---