Understanding Meiosis and Genetic Variation

Sep 2, 2024

Lecture Notes: Meiosis - The Process of Genetic Variety

Introduction

  • Discussed how siblings can look different despite having the same parents.
  • Explanation of meiosis, a process contributing to genetic variety, differing from mitosis.

Mitosis vs. Meiosis

  • Mitosis
    • Creates identical body cells (e.g., skin, stomach cells).
    • Important for growth, repair, and replacing worn out cells.
  • Meiosis
    • Produces gametes (sperm and egg cells), not body cells.
    • Contributes to genetic diversity.

Chromosome Numbers

  • Humans have 46 chromosomes in most body cells.
  • Sperm and egg cells have 23 chromosomes each.
  • Fusion of sperm and egg results in 46 chromosomes.

Reduction Division in Meiosis

  • Starting cell (46 chromosomes) divides into cells with 23 chromosomes.
  • Meiosis is preceded by interphase:
    • Cell growth, DNA replication, and cell processes occur.
    • Chromosomes duplicate from 46 to 92 chromatids.

Stages of Meiosis

  • Meiosis involves two rounds of division: PMAT (Prophase, Metaphase, Anaphase, Telophase) twice.

Meiosis I

  • Prophase I
    • Chromosomes condense and form homologous pairs.
    • Crossing over occurs, exchanging genetic material, creating recombinant chromosomes.
  • Metaphase I
    • Chromosomes align in pairs in the middle of the cell.
  • Anaphase I
    • Chromosomes pulled away by spindle fibers.
  • Telophase I and Cytokinesis
    • Formation of two new cells.

Meiosis II

  • Prophase II
    • No homologous pairs or crossing over.
  • Metaphase II
    • Chromosomes line up in a single file line in the middle.
  • Anaphase II
    • Chromatids are pulled apart.
  • Telophase II and Cytokinesis
    • Resulting in four genetically distinct cells.

Genetic Variation

  • Meiosis produces varied sperm and egg cells due to independent assortment and crossing over.
  • Differences explain why siblings with the same parents can look different.

Chromosomal Errors

  • Nondisjunction: improper separation of chromosomes leading to genetic disorders.
  • A subject of scientific research.

Conclusion

  • Importance of meiosis in contributing to genetic diversity.
  • Encouragement to stay curious about the processes of meiosis.