Lecture on mitosis and meiosis

Nahid Bukhari

Nov 25, 2025 - 13:25

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Both Mitosis and Meiosis are essential types of cell division that allow living organisms to grow, repair, and reproduce. They start with a single parent cell and end with new daughter cells, but they have different goals and outcomes.

🔬 Mitosis: Cell Replication for Growth and Repair

Mitosis is the process that creates two genetically identical cells from one parent cell. Think of it as making a perfect clone.

Basic Description

Purpose: Primarily for growth (increasing the number of cells in an organism) and repair/replacement (replacing old, dead, or damaged cells). It is also the basis of asexual reproduction in some organisms.
Starting Cell: A single diploid ( $2n$ ) parent cell (a cell with two sets of chromosomes, one from each parent). This occurs in most non-reproductive body cells, called somatic cells (like skin, muscle, or liver cells).
Resulting Cells: Two genetically identical daughter cells, which are also diploid ( $2n$ ). The chromosome number remains the same as the parent cell.
Divisions: One single round of division.

Importance (SLO-based)

Objective	Importance of Mitosis
Growth & Development	Produces the vast number of cells needed for an organism to grow from a fertilized egg (zygote) into an adult.
Tissue Repair	Replaces cells damaged by injury or disease, ensuring wounds heal and organs maintain function.
Maintenance & Replacement	Continuously replaces short-lived cells (like skin or blood cells) to keep tissues healthy.
Genetic Stability	Ensures every new somatic cell has an exact, complete, and identical copy of the organism's DNA.

🧬 Meiosis: Cell Replication for Sexual Reproduction

Meiosis is a specialized process that creates four genetically unique cells, each with half the chromosome number of the parent cell.

Basic Description

Purpose: Essential for sexual reproduction. Its goal is to produce gametes (sex cells: sperm in males, eggs in females).
Starting Cell: A single diploid ( $2n$ ) parent cell, but only occurring in germ cells (cells in the reproductive organs).
Resulting Cells: Four genetically unique daughter cells, which are haploid ( $n$ ) (a cell with only one set of chromosomes). The chromosome number is halved.
Divisions: Two consecutive rounds of division (Meiosis I and Meiosis II).
Key Feature: During Meiosis I, a process called crossing over occurs, where homologous chromosomes exchange segments of DNA, leading to new combinations of genes. This is the source of genetic uniqueness.

Objective	Importance of Meiosis
Halving the Chromosome Number	Reduces the chromosome number from diploid ( $2n$ ) to haploid ( $n$ ) so that when two gametes (sperm and egg) fuse during fertilization, the resulting offspring (zygote) restores the correct, constant diploid number for the species.
Genetic Diversity	Introduces genetic variation through crossing over and the independent assortment of chromosomes. This diversity is crucial for a species' long-term survival and adaptation to changing environments.
Formation of Gametes	It is the fundamental process that creates the specialized sex cells (sperm and egg) required for sexual reproduction.

📊 Summary of Differences

Feature	Mitosis	Meiosis
Type of Cell	Somatic (Body) Cells	Germ (Reproductive) Cells
Number of Divisions	One	Two (Meiosis I & II)
Daughter Cells Produced	Two	Four
Chromosome Number	Maintained (Diploid $2n \rightarrow 2n$ )	Halved (Diploid $2n \rightarrow n$ )
Genetic Identity	Genetically Identical to parent and each other	Genetically Unique from parent and each other
Key Role	Growth, Repair, Tissue Maintenance, Asexual Reproduction	Sexual Reproduction, Genetic Diversity