Lecture Notes: Meiosis and Spermatogenesis

Overview of Cell Cycle

• G0 Phase: Cell performs its normal job.
• Interphase: Prepares for cell division, consisting of:
  • G1: Doubling of organelles.
  • S Phase: Doubling of DNA.
  • G2: Production of proteins for cell division.
• Mitosis/Meiosis: Includes Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis.

Meiosis I

Prophase I

• Chromosomes become visible: DNA condenses from chromatin to chromosomes.
• Mitotic Spindle Formation:
  • Centrosomes and centrioles form microtubules.
  • Microtubules attach to centromeres to separate chromosomes.
• Key Events:
  • Synapsis: Homologous chromosomes pair up forming tetrads.
  • Crossing Over: Exchange of genetic material between homologous chromosomes, increasing genetic diversity.

Metaphase I

• Tetrads align on the metaphase plate.

Anaphase I

• Homologous chromosomes are pulled to opposite poles.

Telophase I and Cytokinesis

• Nucleus reforms.
• The physical pinching of cells into two haploid cells.

Meiosis II

• Similar stages: Prophase II, Metaphase II, Anaphase II, Telophase II.
• No recombination: Sister chromatids are separated.
• Results in four genetically unique haploid cells or gametes.

Spermatogenesis

• Process of developing sperm cells.

Key Stages

• Spermatogonium: Stem cells that divide by mitosis.
• Primary Spermatocyte: Enters Meiosis I.
• Secondary Spermatocytes: Enter Meiosis II.
• Spermatids: Undergo spermiogenesis to mature into spermatozoa.

Spermiogenesis

• Maturation of Spermatids:
  • Development of flagellum (tail).
  • Loss of excess cytoplasm.
  • Formation of acrosome cap.
• Spermiation: Release of sperm into the lumen.

Structure of Sperm

• Head: Contains DNA and acrosome with enzymes for egg penetration.
• Midpiece: Contains mitochondria for energy.
• Tail (Flagellum): Used for swimming.

Sperm Production

• Produced at a rate of 300 million per day.
• Life expectancy in the female reproductive tract: approx. 48 hours.

Key Definitions

• Spermatogenesis: Development of sperm.
• Spermiation: Release of mature sperm.
• Diploid/Haploid: Number of chromosome sets.
• Crossing Over: Genetic exchange between homologous chromosomes.
• Tetrad: Four chromatids of a homologous chromosome pair.

Miscellaneous

• Factors affecting pregnancy: Synchronization of ovulation and sperm viability.
• Diagrams and flowcharts illustrating meiosis stages and sperm structure recommended for clarity.