Meiosis: The Process of Cell Division

Overview

• Meiosis is the process of cell division that results in the formation of gametes (sex cells) such as sperm in men and eggs in women.
• Also known as reduction division.
• Consists of two stages: Meiosis I and Meiosis II.

Meiosis I

• Prophase I

  • Begins with a diploid cell.
  • Chromatin replicates and condenses into recognizable x-shaped chromosomes.
  • Chromosomes pair with their counterparts in a process called synapsis forming a tetrad.
  • Crossing over occurs where segments of alleles are exchanged between chromatids, creating new gene combinations.
  • Nuclear membrane disappears and spindle fibers form.

• Metaphase I

  • Homologous chromosomes align at the cell's equator.

• Anaphase I

  • Spindle fibers separate homologous chromosomes, pulling them to opposite poles of the cell.

• Telophase I

  • Chromosomes arrive at opposing poles and remain as sister chromatids.
  • Nuclear envelope reforms and spindle fibers disappear.
  • Cytokinesis occurs, ending Meiosis I with two genetically distinct haploid daughter cells.

Meiosis II

• Prophase II

  • DNA is not replicated before Meiosis II begins.
  • Nuclear envelope disappears and spindle fibers form.

• Metaphase II

  • Chromosomes align at the equator and attach to spindle fibers.

• Anaphase II

  • Sister chromatids separate and move to opposite poles.
  • Once separated, they are referred to as chromosomes.

• Telophase II

  • Spindle fibers disappear, and the nuclear membrane reforms.
  • Cytokinesis occurs, resulting in four genetically distinct haploid daughter cells, each containing one set of chromosomes.

Key Points

• Meiosis results in genetic diversity through crossing over and independent assortment.
• Ends with four non-identical haploid cells, essential for sexual reproduction.