Phases of Meiosis

Jul 8, 2024

Meiosis Phases

Introduction to Meiosis

  • Meiosis: Also called reduction division; produces gametes (sex cells: sperm in males, eggs in females).
  • Stages of Meiosis: Meiosis I and Meiosis II, each with four phases.

Phases of Meiosis I

Prophase I

  • Starts with a diploid cell (two sets of chromosomes, one from each parent).
  • Chromosomes replicate and condense into the familiar X shape.
  • Homologous chromosomes pair up and form tetrads (group of four sister chromatids).
  • Synapsis: Process where homologous chromosomes bind together.
  • Crossing Over: Exchange segments of alleles between chromatids, leading to genetic variety.
  • Nuclear membrane disappears, centrioles move to opposite ends, spindle fibers form.

Metaphase I

  • Homologous chromosomes line up at equator, attach to spindle fibers from opposite poles.

Anaphase I

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

Telophase I

  • Chromosomes at separate poles, each still consists of sister chromatids.
  • Nuclear membrane reforms, spindle fibers disappear.
  • Cytokinesis occurs, resulting in two genetically different haploid daughter cells.

Phases of Meiosis II

Prophase II

  • Similar to Prophase I but without DNA replication.
  • Nuclear membrane disappears, spindle fibers form from centrioles.

Metaphase II

  • Chromosomes in each cell line up at equator, attach to spindle fibers from both poles.

Anaphase II

  • Sister chromatids separate and move to opposite poles, become individual chromosomes.

Telophase II

  • Spindle fibers disappear, nuclear membranes reform.
  • Cytokinesis occurs in each cell, resulting in four genetically different haploid daughter cells.

Key Points About Meiosis

  • Begins with a diploid cell and produces four genetically different haploid gametes.
  • Gametes are sperm in males and eggs in females.
  • Homologous chromosomes separate during Meiosis I to produce haploid cells.
  • Sister chromatids separate during Meiosis II to become individual chromosomes.
  • Crossing over during Prophase I leads to genetic diversity.