Lecture Notes: Meiosis II

Overview

• Focus: Meiosis II (continuation from Meiosis I)
• Purpose: To separate chromatids in each of the two cells from Meiosis I into four haploid cells.
• Structure of Meiosis II: Similar stages to mitosis, but starting with two cells.

Phases of Meiosis II

Prophase II

• Objective: Prepare the cell for division.
• Key Features:
  • No crossing over (homologous partners are separated).
  • Spindle fibers form.
  • Centrioles move to opposite poles.
  • Recombinant chromosomes are visible (contain bits from different chromosomes).

Metaphase II

• Objective: Align chromosomes for segregation.
• Key Features:
  • Recombinant chromosomes line up at the cell's equator.
  • Spindle fibers attach to centromeres.
  • Chromosomes are lined up as individuals (not in pairs).

Anaphase II

• Objective: Separate chromatids into individual chromosomes.
• Key Features:
  • Spindle fibers contract.
  • Separation of chromatids into single stranded chromosomes.
  • Chromatids are now referred to as individual chromosomes.

Telophase II

• Objective: Finalize cell division.
• Key Features:
  • Nuclear membranes reform around the four sets of chromosomes.
  • Cytokinesis occurs, dividing the cells completely into four non-identical haploid cells.
  • Chromosomes are single stranded in each new cell.

Summary of Meiosis Process

• Meiosis I:
  • Starts with diploid cells.
  • Ends with two haploid cells; chromosomes replicate and cross over.
• Meiosis II:
  • Separates chromatids into individual chromosomes.
  • Ends with four non-identical haploid cells.

Key Terminology

• Random Arrangement: Chromosomes line up randomly at the equator.
• Cytokinesis: Division of cytoplasm, resulting in four separate cells.
• Diploid: Full set of chromosomes (in humans 46).
• Haploid: Half the set of chromosomes (in humans 23).
• Recombinant Chromosomes: Chromosomes that underwent crossing over.
• Single-Stranded Chromosomes: Result from separation of chromatids.

Conclusion

• Meiosis II ensures genetic diversity and correct chromosome number in gametes.
• Understanding stages helps in studying genetic variations and potential errors in cell division.
• Reminder to review related videos and practice exam questions for better understanding.