Lecture Notes: Mitosis vs Meiosis

Introduction

• Biological processes often have similar sounding terms (e.g., Chromosome, Chromatid, Chromatin, Transcription, Translation, Mitosis, Meiosis).
• Comparison of mitosis and meiosis is crucial for understanding their similarities, differences, and significance.
• This lecture provides a side-by-side comparison using a split-screen approach.

Key Concepts

• Both Processes: Involved in creating new cells, with mitosis producing body cells and meiosis producing gametes (sperm and egg cells).
• Starting Cell: Both processes start with a diploid cell (2n) which, in humans, has 46 chromosomes (23 from each parent).
• Interphase: Critical preparatory phase where chromosomes are duplicated.

Stages of Mitosis and Meiosis

• Acronym: PMAT (Prophase, Metaphase, Anaphase, Telophase) helps remember stages.
• Mitosis goes through PMAT once; Meiosis goes through PMAT twice (Meiosis I and II).

Mitosis

1. Prophase

   • Chromosomes condense and become visible.
   • Nuclear envelope breaks down.

2. Metaphase

   • Chromosomes align in the middle in a single file line.

3. Anaphase

   • Chromatids pulled apart to opposite sides of the cell.

4. Telophase

   • Chromosomes reach opposite ends; nuclear membranes reform.
   • Followed by cytokinesis, resulting in two identical diploid cells.

Meiosis I

1. Prophase I

   • Chromosomes condense and pair with homologous chromosomes.
   • Crossing over occurs, allowing genetic exchange (recombinant chromosomes).

2. Metaphase I

   • Chromosome pairs line up in the middle.

3. Anaphase I

   • Homologous chromosomes are pulled to opposite sides (not chromatids).

4. Telophase I

   • Chromosomes at opposite ends; new nuclei form.
   • Followed by cytokinesis.

Meiosis II

1. Prophase II

   • Chromosomes condense again.

2. Metaphase II

   • Chromosomes line up in the middle in a single file line.

3. Anaphase II

   • Chromatids are pulled to opposite sides.

4. Telophase II

   • Chromosomes reach opposite ends; new nuclei form.
   • Followed by cytokinesis, resulting in four non-identical haploid gametes.

Significance of Meiosis

• Results in genetic diversity due to crossing over and independent assortment.
• Produces gametes with half the number of chromosomes (haploid) as the original cell.
• When sperm and egg combine, they form a diploid zygote, beginning a new organism's development.

Conclusion

• Mitosis is essential for growth and cell replacement, whereas meiosis is crucial for sexual reproduction and genetic diversity.
• Explore more details beyond this foundational overview.