Meiosis Lecture Notes

Introduction

• Importance of genetic variation between siblings
• Focus on meiosis, the process contributing to genetic diversity
• Brief distinction from mitosis:
  • Mitosis produces identical body cells (e.g., skin, stomach cells)
  • Meiosis produces gametes (sperm and egg cells)

Chromosome Basics

• Humans typically have 46 chromosomes in body cells
• Sperm and egg cells contain 23 chromosomes each
• Fusion of sperm and egg restores the chromosome number to 46
• Meiosis is a reduction division, reducing the chromosome number from 46 to 23

Interphase

• Pre-Meiosis stage:
  • Known as interphase
  • Cells grow, replicate DNA, and carry out cell processes
• DNA duplication leads to 46 chromosomes with 92 chromatids (counted by centromeres)

Stages of Meiosis

Meiosis I

• Prophase I:
  • Chromosomes condense, line up with homologous pairs
  • Crossing over occurs, exchanging genetic material (recombinant chromosomes)
• Metaphase I:
  • Chromosome pairs align in the middle of the cell
• Anaphase I:
  • Chromosome pairs pulled away by spindle fibers
• Telophase I:
  • Formation of two nuclei
  • Cytokinesis divides the cytoplasm, forming two new cells

Meiosis II

• Prophase II:
  • Chromosomes and spindles form
  • No crossing over
• Metaphase II:
  • Chromosomes line up in a single file in the middle
• Anaphase II:
  • Chromatids are pulled to opposite sides
• Telophase II:
  • Reformation of nuclei
  • Cytokinesis results in four distinct cells

Outcome of Meiosis

• Produces sperm cells in males, egg cells in females
• Genetic variety due to independent assortment and crossing over
• Each sperm or egg is unique, contributing to sibling diversity

Additional Note: Nondisjunction

• Error during meiosis where chromosomes don't separate properly
• Can lead to genetic disorders
• Subject of ongoing scientific study

Conclusion

• Meiosis is crucial for genetic diversity in offspring
• It involves complex processes that ensure variation
• Continuous scientific interest due to potential for errors in chromosome separation

Reminder: Stay curious!