Phases of Meiosis

May 28, 2024

Phases of Meiosis

Introduction to Meiosis

  • Meiosis: Also known as reduction division.
  • Purpose: Produces gametes (sex cells - sperm in males, eggs in females).
  • Two stages: Meiosis I and Meiosis II.

Meiosis I

Phases of Meiosis I

  1. Prophase I

    • Starts with a diploid cell.
    • Chromatin contains two sets of chromosomes (one from each parent).
    • DNA replication occurs, forming X-shaped chromosomes with identical sister chromatids.
    • Synapsis: Homologous chromosomes pair up, forming a tetrad (4 sister chromatids).
    • Crossing over: Exchange of alleles between chromatids of homologous chromosomes, resulting in genetic recombination.
    • Disappearance of nuclear membrane, movement of centrioles to opposite poles, formation of spindle fibers.
  2. Metaphase I

    • Homologous chromosomes line up at the equator.
    • Chromosomes attach to spindle fibers from opposite poles.
  3. Anaphase I

    • Spindle fibers pull homologous chromosomes to opposite poles.
  4. Telophase I

    • Chromosomes (each with sister chromatids) move to opposite poles.
    • Nuclear membrane reforms, spindle fibers disappear.
    • Followed by cytokinesis, resulting in two genetically different haploid daughter cells.

Meiosis II

  • Unlike Meiosis I, DNA does not replicate before Meiosis II.

Phases of Meiosis II

  1. Prophase II

    • Nuclear membrane disappears, spindle fibers fan out.
  2. Metaphase II

    • Chromosomes line up at the equator.
    • Attach to spindle fibers from both poles.
  3. Anaphase II

    • Sister chromatids separate, moving to opposite poles.
    • Once separated, they are called chromosomes.
  4. Telophase II

    • Nuclear membrane reforms.
    • Cytokinesis occurs in both cells, resulting in four genetically different haploid daughter cells.

Key Points

  • Meiosis starts with a diploid cell and produces haploid gametes.
  • Gametes are genetically different.
  • Meiosis I: Separation of homologous chromosomes.
  • Meiosis II: Separation of sister chromatids.

Prophase I Highlights

  • Synapsis: Pairing of homologous chromosomes.
  • Tetrad: Four chromatids of homologous chromosomes.
  • Crossing over: Exchange of alleles, resulting in genetic variation.
  • All gametes produced are haploid.