Overview of Meiosis and Gamete Production

Overview of Meiosis

• Meiosis is a type of cell division that specifically produces gametes.
• It occurs in the sex gonads: ovaries (for eggs) and testes (for sperm).
• Meiosis involves germline cells in these organs that divide to generate haploid gametes.

Stages of Meiosis

Meiosis I

• Prophase I
  • Crossing Over: DNA is exchanged between homologous chromosomes, which increases genetic diversity.
• Metaphase I
  • Synapsed pairs of homologous chromosomes align at the metaphase plate.
• Anaphase I
  • Homologous pairs separate and move to opposite poles of the cell.
• Telophase I and Cytokinesis
  • Sister chromatids remain attached; the cell divides into two haploid cells.

Meiosis II

• Prophase II
  • Chromosomes condense, spindle fibers form again.
• Metaphase II
  • Chromosomes align at the metaphase plate.
• Anaphase II
  • Sister chromatids separate and move to opposite poles.
• Telophase II and Cytokinesis
  • Four distinct haploid gametes are produced from one original cell.

Gamete Production

• Oogenesis (Egg Production)
  • In females, meiosis results in one viable egg and polar bodies.
• Spermatogenesis (Sperm Production)
  • In males, meiosis results in four viable sperm from one original cell.

Genetic Diversity Mechanisms in Gametes

1. Crossing Over
   • Occurs in Prophase I where homologous pairs exchange DNA, enhancing genetic variation.
2. Independent Assortment
   • The random distribution of maternal and paternal chromosomes into gametes, increasing variety.
3. Fertilization
   • The random union of gametes from different parents creates genetic diversity in the offspring.
   • Resulting fertilized egg is a diploid zygote containing 23 pairs of chromosomes—one from each parent.

Nondisjunction in Meiosis

• Nondisjunction is the failure of chromosomes to separate properly during meiosis, leading to gametes with abnormal chromosome numbers, which can result in genetic disorders or anomalies.

Comparison of Meiosis and Mitosis

• Mitosis leads to two identical diploid cells, while meiosis results in four genetically distinct haploid gametes.