Cell Division Types: Mitosis and Meiosis

Cell Division

• Cell division is the process where a single cell divides into two or more daughter cells, crucial for growth, repair, and reproduction.

Types of Cell Division

• Mitosis: Produces two genetically identical diploid daughter cells from a single diploid parent cell, vital for somatic cell growth and repair.
  • Key phases: Prophase, Metaphase, Anaphase, Telophase.
  • Result: Two identical diploid daughter cells.
• Meiosis: Produces four genetically unique haploid daughter cells from a single diploid parent cell, critical for sexual reproduction, forming gametes (sperm and egg).
  • Two rounds of division: Meiosis I and Meiosis II.
  • Result: Four unique haploid daughter cells.

Mitosis

• Interphase: The cell cycle period before mitosis, where the cell grows, replicates its DNA, and prepares to divide.
  • Subphases: G1, S, and G2 phase.
• Prophase: Chromosomes condense becoming visible, nuclear envelope breaks down, and spindle fibers form.
• Metaphase: Chromosomes align at the cell's equator (metaphase plate).
• Anaphase: Sister chromatids separate and move to opposite poles of the cell.
• Telophase: Chromosomes decondense, nuclear envelope reforms, and cell division begins.
• Cytokinesis: Cytoplasm divides, forming two separate daughter cells.

Meiosis

• Meiosis I: The first division, separating homologous chromosomes.
  • Prophase I: Homologous chromosomes pair up (synapsis), exchange genetic material (crossing over), a key source of genetic variation.
  • Metaphase I: Homologous pairs align at the metaphase plate. Independent assortment occurs, further increasing genetic diversity.
  • Anaphase I: Homologous chromosomes separate and move to opposite poles.
  • Telophase I: Chromosomes decondense, nuclear envelope may reform, and cell division starts. Cytokinesis forms two haploid daughter cells.
• Meiosis II: The second division, similar to mitosis, separating sister chromatids.
  • Prophase II: Chromosomes condense, nuclear envelope breaks down (if reformed).
  • Metaphase II: Chromosomes align at the metaphase plate.
  • Anaphase II: Sister chromatids separate and move to opposite poles.
  • Telophase II: Chromosomes decondense, nuclear envelope reforms, and cytokinesis forms four haploid daughter cells.

Significance of Cell Division

• Growth and Development: Critical for organisms to grow larger and develop from a single fertilized egg.
• Tissue Repair and Replacement: Essential for repairing damaged tissues and replacing old cells.
• Asexual Reproduction: Some organisms reproduce asexually via cell division, producing genetically identical offspring.
• Sexual Reproduction: Essential for creating gametes (sperm and egg), which combine to form genetically unique offspring.
• Genetic Diversity: Meiosis, through crossing over and independent assortment, creates genetic variation among offspring, vital for adaptation and evolution.

Regulation of Cell Division

• Cyclins and Cyclin-Dependent Kinases (CDKs): Proteins regulating cell cycle progression. Cyclin levels fluctuate, activating CDKs.
• Checkpoints: Control points in the cell cycle. Errors (DNA damage) halt the cycle.
• Cancer: Uncontrolled cell division leading to tumors. Dysregulation of cell cycle control is a major cancer factor.