Lecture on Meiosis

Introduction

• Topic: Understanding how siblings with the same parents can appear different.
• Focus: The process called meiosis.
• Comparison: Not to be confused with mitosis.
  • Mitosis: Produces identical body cells (e.g., skin, stomach) for growth and repair.
  • Meiosis: Contributes to genetic variety, produces gametes (sperm and egg cells).

Chromosome Basics

• Human Body Cells: 46 chromosomes.
• Gametes (Sperm and Egg): 23 chromosomes each.
  • Combined to make 46 chromosomes in a fertilized egg.
• Meiosis: Reduction division process from 46 to 23 chromosomes.

Pre-Meiosis: Interphase

• Interphase: Occurs before meiosis starts.
  • Cell grows, replicates DNA, and carries out processes.
  • Chromosomes duplicate from 46 to 92 chromatids but remain 46 due to centromere counting.

Stages of Meiosis

Meiosis I

• Prophase I:
  • Chromosomes condense, line up with homologous pairs.
  • Crossing Over: Exchange of genetic information for variety.
• Metaphase I:
  • Chromosomes line up in pairs at the middle of the cell.
• Anaphase I:
  • Chromosomes pulled away by spindle fibers.
• Telophase I:
  • Formation of two nuclei, leading to two new cells.
  • Followed by cytokinesis to split cytoplasm.

Meiosis II

• Prophase II:
  • Chromosomes and spindles form, no homologous pairs or crossing over.
• Metaphase II:
  • Chromosomes line up in a single file in the middle.
• Anaphase II:
  • Chromatids pulled away to opposite sides.
• Telophase II:
  • Formation of four cells, followed by cytokinesis.

Gamete Production and Genetic Variety

• Males: Produces four different sperm cells each time.
• Females: Produces egg cells.
• Outcome: Each gamete is genetically unique, contributing to sibling variety.

Nondisjunction and Genetic Disorders

• Nondisjunction: Failure of chromosomes to separate correctly.
  • Can lead to genetic disorders.
• Research: Scientists study meiosis to understand these disorders.

Conclusion

• Reminder: Meiosis is critical for genetic diversity among siblings.
• Encouragement: Stay curious about biological processes.