Mitosis and Meiosis

Overview

Mitosis and meiosis are two essential processes for cell replication in organisms. Mitosis results in two identical daughter cells, while meiosis creates four genetically different cells used in sexual reproduction.

Mitosis

• Purpose: Simple duplication of a cell, resulting in two identical daughter cells with the same genetic material as the original cell.
• Key Points:
  • Equational division, maintains chromosome number.
  • Responsible for growth, repair, and asexual reproduction.

Phases of Mitosis

1. Interphase: Preparation phase for cell division, involving protein synthesis, DNA duplication, and enzyme production.
2. Mitosis: Divided into two main processes:
   • Karyokinesis (division of the nucleus)
   • Cytokinesis (division of the cytoplasm)

Steps of Karyokinesis

• Prophase: Chromosomes condense, nuclear envelope disintegrates, spindle apparatus forms.
• Metaphase: Chromosomes align at a central axis, attached to spindle fibers at centromeres.
• Anaphase: Chromosomes separate, moving to opposite cell poles.
• Telophase: Nuclear envelopes reform around separated chromosomes, cell begins to divide.

Significance of Mitosis

• Maintains genetic continuity across cells.
• Facilitates growth and tissue repair.
• Uncontrolled mitosis can lead to tumors or cancer.

Meiosis

• Purpose: To produce gametes (sperm and eggs) with half the genetic material of the original cell, promoting genetic diversity.

Phases of Meiosis

1. Interphase: DNA replication; chromosomes are duplicated.
2. Meiosis I: Homologous chromosomes separate.
   • Prophase I: Chromosomes pair and exchange DNA (crossing over), forming tetrads.
   • Metaphase I: Homologous pairs align at the metaphase plate.
   • Anaphase I: Homologous chromosomes pulled to opposite poles.
   • Telophase I: Cell divides into two, each with half the number of chromosomes.
3. Meiosis II: Sister chromatids separate.
   • Prophase II: Chromosomes condense, new spindles form.
   • Metaphase II: Chromosomes align at the metaphase plate.
   • Anaphase II: Sister chromatids separate and move to opposite poles.
   • Telophase II: Cells divide again, resulting in four haploid cells.

Significance of Meiosis

• Reduces chromosome number by half in gametes, essential for sexual reproduction.
• Increases genetic variation through recombination and independent assortment.

Conclusion

Mitosis and meiosis are critical cellular processes for life. Mitosis maintains genetic stability, while meiosis increases genetic diversity, both essential for the survival and evolution of species.