Mitosis and Meiosis

• Cell division includes mitosis, which produces identical cells, and meiosis, which produces genetically unique gametes.

Mitosis (Asexual Reproduction & Growth)

• Produces identical cells for growth, repair, and asexual reproduction.
• The chromosome number of the parent cell is maintained.

Phases of Mitosis

• Prophase: Chromosomes condense, the nuclear membrane dissolves, and spindle fibers form.
• Metaphase: Chromosomes align at the cell’s equator.
• Anaphase: Sister chromatids separate and move to opposite poles.
• Telophase: Nuclear membranes reform, and chromosomes decondense.
• Cytokinesis: The cell splits into two identical diploid (2n) daughter cells.

Key Characteristics of Mitosis

• One division occurs.
• Two identical diploid (2n) cells are produced.
• There is no genetic variation.
• Occurs in somatic (body) cells.
• Used for growth, repair, and asexual reproduction.

Meiosis (Sexual Reproduction)

• Produces genetically diverse gametes (sperm and egg cells) with half the chromosome number of the parent cell.
• Genetic variation occurs through recombination and independent assortment.

Phases of Meiosis

• Meiosis I (Reductional Division):
  • Prophase I: Chromosomes condense, homologous chromosomes pair up (synapsis), and crossing over occurs.
  • Metaphase I: Homologous pairs align at the equator.
  • Anaphase I: Homologous chromosomes separate to opposite poles.
  • Telophase I & Cytokinesis: Two haploid (n) cells form.
• Meiosis II (Equational Division):
  • Prophase II: Chromosomes condense, and spindle fibers form.
  • Metaphase II: Chromosomes align at the equator.
  • Anaphase II: Sister chromatids separate.
  • Telophase II & Cytokinesis: Four genetically unique haploid (n) cells form.

Key Characteristics of Meiosis

• Two divisions occur.
• Four genetically unique haploid (n) cells are produced.
• Genetic variation is due to crossing over and independent assortment.
• Occurs in reproductive cells (gametes).
• Used for sexual reproduction.

Key Differences: Mitosis vs. Meiosis

• Purpose: Mitosis is for growth, repair, and asexual reproduction, while meiosis is for the formation of gametes.
• Number of Divisions: Mitosis involves 1 division, whereas meiosis involves 2.
• Number of Daughter Cells: Mitosis produces 2 daughter cells, and meiosis produces 4.
• Chromosome Number: Mitosis results in diploid (2n, same as parent) cells, while meiosis results in haploid (n, half of parent) cells.
• Genetic Variation: Mitosis has no genetic variation (identical cells), but meiosis does (crossing over & independent assortment).
• Occurs In: Mitosis occurs in somatic (body) cells, and meiosis occurs in gametes (sex cells).

Why is Meiosis Important?

• Genetic Variation: Ensures diversity in offspring through recombination and independent assortment.
• Maintains Chromosome Number: Prevents doubling of chromosomes in each generation by reducing it to half in gametes.
• Essential for Evolution: Provides genetic differences that drive natural selection.

Conclusion

• Mitosis allows organisms to grow and heal by producing identical cells. Meiosis is essential for sexual reproduction and genetic diversity.