Meiosis Lecture Notes

Introduction

• Discussion on why siblings can look different despite having the same parents.
• Meiosis: Process responsible for genetic variety, unlike mitosis which creates identical body cells for growth and repair.
  • Meiosis produces sperm and egg cells (gametes).
• Humans have 46 chromosomes in most body cells.
  • Sperm and egg cells have 23 chromosomes each.
  • Fertilization combines them to 46 chromosomes, forming a human.

Meiosis Overview

• Reduction Division: Starts with 46 chromosomes, ends with gametes having 23.
• Interphase: Precedes meiosis (same as mitosis), where:
  • Cell grows, replicates DNA and organelles.
  • Chromosomes duplicate from 46 to 92 chromatids, but still counted as 46 chromosomes due to centromeres.

Phases of Meiosis

Meiosis I

• Prophase I:
  • Chromosomes condense, pair with homologous chromosomes.
  • Crossing Over: Exchange of genetic material between homologous chromosomes, leading to recombinant chromosomes and genetic diversity.
• Metaphase I: Homologous chromosome pairs align in the cell's center.
• Anaphase I: Chromosomes pulled away by spindle fibers.
• Telophase I: Two nuclei form, followed by cytokinesis, resulting in two cells.

Meiosis II

• Prophase II: Similar to prophase I but lacks crossing over.
• Metaphase II: Chromosomes line up single file in the cell's center.
• Anaphase II: Chromatids pulled away.
• Telophase II: Nuclei reform, followed by cytokinesis, resulting in four different gametes.

Genetic Diversity

• Independent Assortment and Crossing Over result in genetic variety.
• In males, meiosis produces four distinct sperm cells.
• In females, produces egg cells.

Nondisjunction

• Discussion on the potential errors in meiosis when chromosomes do not separate correctly.
• Nondisjunction: Leads to genetic disorders due to incorrect chromosome number.

Conclusion

• Meiosis is crucial for genetic diversity and proper formation of gametes.
• Encouragement to continue studying and exploring these biological processes.