Meiosis Process

Meiosis - Process of Nuclear and Cellular Division

• Meiosis is a 2-stage process of nuclear and cellular division, resulting in four haploid cells.
• Stage 1: Meiosis I
  • Prophase I: Tetrad formation through synapsis of homologous chromosomes.
  • Metaphase I: Tetrads line up at the metaphase plate.
  • Anaphase I: Homologous chromosomes separate, resulting in haploid cells.
  • Telophase I: Nuclear envelope reforms, and chromatin becomes less visible.
• Stage 2: Meiosis II
  • Prophase II: Preparation for the second round of cell division.
  • Metaphase II: Sister chromatids line up at the metaphase plate.
  • Anaphase II: Sister chromatids separate, resulting in four haploid daughter cells.
  • Telophase II: Nuclear envelope reforms, and chromatin becomes less visible.

Differences Between Mitosis and Meiosis

• Mitosis: A process of cell division that results in two diploid cells.
• Meiosis: A process of cell division that results in four haploid cells.
• Key differences:
  • Synapsis of homologous chromosomes occurs in meiosis, but not in mitosis.
  • Crossover occurs in meiosis, but not in mitosis.
  • Homologous chromosomes line up at the metaphase plate in meiosis, but not in mitosis.
  • Sister chromatids line up at the metaphase plate in both mitosis and meiosis.

Mitosis - Division of the Nucleus or Karyokinesis

• Interphase: Chromosomes are loosely coiled and not visible, and centrosomes begin to separate.
• Prophase: Chromosomes become visible, centrosomes move to opposite poles, and nuclear membrane breaks down.
• Metaphase: Chromosomes line up at the center of the cell, and spindle fibers attach to centromeres.
• Anaphase: Sister chromatids separate and move to opposite poles of the cell.
• Telophase: Spindle fibers disappear, nuclear membranes form, and chromosomes become less visible.

Cell Cycle Overview

• G2: Cell double checks duplicated chromosomes for errors, making any needed repairs.
• S: Each of the 46 chromosomes is duplicated by the cell.
• G1: Cellular contents, excluding chromosomes, are duplicated.
• Go: Cell cycle arrest.

Chromosomes vs. Chromatids - Structure

• Chromosomes: Made up of two chromatids joined at the centromere.
• Chromatids: One-half of a replicated chromosome.
• Autosomes: First 22 pairs of chromosomes.
• Allosomes: Last pair of chromosomes, also known as sex chromosomes.

Spindle Fibers - Chromatids on the Move

• Mitotic spindle: Polymerization of tubulin molecules to form microtubules originating at the centrioles.
• Kinetochore fibers: Extend from the pole of the spindle to the centromere of the chromosome to which they attach.