mitosis and meiosis

Mitosis and Meiosis Overview

  • Cell Division: Key phase of cell cycle; consists of interphase, nuclear division (karyokinesis), and cytokinesis.

Interphase

  • Resting Phase: Between successive mitotic divisions.

  • Stages: Divided into G₁, S, and G₂.

    • G₁: Major growth and synthesis of substances.

    • S (Synthesis): DNA replication.

    • G₂: Formation of structures involved in mitosis (e.g., spindle fibers).

M-Phase (Mitosis or Meiosis)

  • Karyokinesis: First, the nucleus divides.

  • Cytokinesis: Cytoplasm separates into two halves.

Key Terminologies

  • Chromosome: Structure containing genes; consists of DNA and proteins.

  • Chromatid: One copy of a replicated chromosome.

  • Centromere: Region that joins sister chromatids; site for kinetochore attachment.

  • Kinetochore: Protein disk linking chromatids to spindle.

  • Spindle Apparatus: Microtubules forming during prophase to separate chromosomes.

  • Homologous Chromosomes: Pairs with equivalent genes in diploid cells.

Mitosis Detailed Process

  • Prophase: Chromosomes condense, spindle fibers form.

  • Metaphase: Chromosomes align at the cell's equator.

  • Anaphase: Sister chromatids separate and move to poles.

  • Telophase: Nuclear envelope reforms, 2 identical nuclei formed.

Importance of Mitosis

  • Maintains genetic consistency across daughter cells; essential for growth and development.

Meiosis Overview

  • Definition: Nuclear division resulting in halved chromosome number during gamete formation.

  • Unique Features: Synapsis, homologous recombination, reduction division.

Stages of Meiosis

  • Prophase I: Long and complicated; subdivided into Preleptonema, Leptonema, Zygonema, Pachynema, Diplonema, Diakinesis.

  • Metaphase I: Bivalents align at spindle equator.

  • Anaphase I: Homologous chromosomes move to opposite poles.

  • Telophase I: Two daughter nuclei form; nuclear membrane reappears.

  • Interkinesis: Short phase between divisions, no DNA replication.

Differences Between Mitosis and Meiosis

  • Mitosis: Somatic cells, one division, two genetically identical daughter cells.

  • Meiosis: Germ cells, two divisions, four genetically diverse daughter cells.

Similarities and Differences Recap

  • Similarities: Both processes involve spindle apparatus and disintegration of nuclear membrane.

  • Differences: Cross-over in meiosis, reduction division, and stages of prophase in meiosis are more complex.

Visual Diagram of Stages

  • Stages of meiosis illustrated\ (not included in notes).