Meiosis

Meiosis has eight stages and results in the formation of gametes (sex cells with half the number of chromosomes of a normal cell).

• Prophase I of meiosis is similar to prophase of mitosis. The difference is that homologous chromosomes (each homologue is from a different parent) attach to form tetrads. The exchange of genetic material between homologous chromosomes, or crossing-over, occurs.
  
  
• In metaphase I tetrads line up in the middle of the cell and spindle fibers attach to each centromere.
  
  
• In anaphase I one homologue is pulled to each pole.
  
  
• In telophase I the nuclei are reorganized and the chromosomes are decondensed. This phase is followed by a special meiotic interphase where no DNA replication occurs.
  
  
• In prophase II the nucleus disappears and the chromosomes condense.
  
  
• In metaphase II the chromosomes line up in the middle of the cell and the spindle fibers attach to kinetichore proteins.
  
  
• In anaphase II the chromosomes separate and the chromatids are pulled to the poles. Each cell now has half as many chromosomes as it used to.
  
  
• In telophase II the nucleus is reorganized, the chromosomes are decondensed, the centrioles do not replicate, and the cell remains in the G₁ phase.