Cellular Reproduction: Mitosis and Meiosis

Cellular Reproduction: Mitosis and Meiosis

• Cellular reproduction is essential for growth, repair, and reproduction in organisms. Two primary methods are mitosis and meiosis.

• Mitosis: A type of cell division that produces two genetically identical daughter cells from a single parent cell. Crucial for growth and repair.

  • Phases of Mitosis:

• Interphase: The cell grows, replicates its DNA, and prepares for division.

• Prophase: Chromosomes condense and become visible; the nuclear envelope breaks down; spindle fibers form.

• Metaphase: Chromosomes align along the equator of the cell.

• Anaphase: Sister chromatids separate and move to opposite poles of the cell.

• Telophase: Chromosomes decondense; nuclear envelopes reform; spindle fibers disassemble.

• Cytokinesis: The cytoplasm divides, creating two separate daughter cells.

  • Characteristics of Mitosis:

• Results in two diploid daughter cells.

• Daughter cells are genetically identical to the parent cell.

• Maintains the chromosome number in daughter cells.

• Used for somatic (body) cell replication.

• Meiosis: A type of cell division that produces four genetically unique daughter cells from a single parent cell. Essential for sexual reproduction.

  • Phases of Meiosis:

• Meiosis I:

• Prophase I: Homologous chromosomes pair up (synapsis) and crossing over (genetic recombination) occurs.

• Metaphase I: Homologous chromosome pairs align along the equator of the cell.

• Anaphase I: Homologous chromosomes separate and move to opposite poles of the cell.

• Telophase I: Chromosomes arrive at the poles; nuclear membranes may reform; the cell divides into two daughter cells.

• Meiosis II:

• Prophase II: Chromosomes condense; nuclear envelopes (if reformed) break down; spindle fibers form.

• Metaphase II: Individual chromosomes align along the equator of the cell.

• Anaphase II: Sister chromatids separate and move to opposite poles of the cell.

• Telophase II: Chromosomes decondense; nuclear envelopes reform; spindle fibers disassemble; cytokinesis occurs, resulting in four haploid daughter cells.

  • Characteristics of Meiosis:

• Results in four haploid daughter cells.

• Daughter cells are genetically unique due to crossing over and independent assortment.

• Reduces the chromosome number by half from the parent cell.

• Used for gamete (sperm and egg) production.

• Key Differences between Mitosis and Meiosis:

• Chromosome Number: Mitosis maintains the chromosome number, while meiosis reduces it by half.

• Genetic Variation: Mitosis produces genetically identical cells, while meiosis results in genetically unique cells.

• Number of Divisions: Mitosis involves one division, while meiosis involves two divisions.

• Purpose: Mitosis is for growth and repair, whereas meiosis is for sexual reproduction.

• Importance of Reproduction

• Genetic Diversity: Meiosis provides genetic diversity for adaptation and evolution.

• Growth and Repair: Mitosis enables growth and repair of tissues in multicellular organisms.

• Sexual Reproduction: Meiosis is critical in sexual reproduction for generating genetically unique offspring.

• Cytokinesis: Division of the cytoplasm following nuclear division (mitosis or meiosis).

  • Differing mechanisms for animal and plant cells.
  • Cleavage furrow in animal cells.
  • Cell plate formation in plant cells.

• Genetic Material: Prior to both mitosis and meiosis, DNA replication occurs, ensuring each daughter cell receives a complete set of genetic instructions.