Notes on Meiosis Lecture

Introduction

• Topic: Meiosis - process that creates genetic variation
• Difference from Mitosis:
  • Mitosis creates identical body cells (e.g., skin, stomach cells)
  • Meiosis creates gametes (sperm and egg cells)

Key Concepts

• Chromosomes in Humans:
  • Human body cells: 46 chromosomes
  • Sperm and egg cells: 23 chromosomes each
  • Fusion of sperm and egg leads to 46 chromosomes in fertilized egg
• Meiosis as Reduction Division:
  • Starts with a cell having 46 chromosomes, ends with gametes having 23 chromosomes

Interphase

• Precedes both meiosis and mitosis:
  • Cell growth, DNA replication
  • Chromosome duplication occurs, resulting in 46 chromosomes (92 chromatids)

Stages of Meiosis

• Meiosis I:
  • Involves two rounds of PMAT (Prophase, Metaphase, Anaphase, Telophase)
  • Chromosome count reduces from 46 to 23

Prophase I

• Chromosomes condense and thicken
• Homologous pairs line up
• Crossing Over:
  • Genetic exchange between homologous chromosomes
  • Results in recombinant chromosomes, contributing to genetic diversity

Metaphase I

• Chromosomes (in pairs) align in the middle of the cell

Anaphase I

• Chromosomes pulled away by spindle fibers

Telophase I

• Formation of two nuclei

• Cytokinesis: Splitting of cytoplasm, resulting in two new cells

• Meiosis II:

  • Similar to mitosis, but starts from cells with 23 chromosomes

Prophase II

• Chromosomes present, no homologous pairs, no crossing over occurs

Metaphase II

• Chromosomes align in single file line in the middle of the cell

Anaphase II

• Sister chromatids pulled apart to opposite sides

Telophase II

• Nuclei reform, resulting in four cells

Final Notes

• Meiosis in Males vs. Females:
  • Males: Produces sperm cells
  • Females: Produces egg cells
• Genetic Variation:
  • Due to independent assortment and crossing over
  • Siblings can be genetically different despite sharing parents
• Nondisjunction:
  • Incorrect chromosome separation
  • May lead to genetic disorders, ongoing area of research

Conclusion

• Encouragement to stay curious about biological processes.