Lecture on Sexual Reproduction and Fertilization

Overview of Sex Cells

• Sexual Reproduction: Involves combining genetic material from two parents.
• Sex Cells (Gametes): Specialized cells that carry genetic material.
  • Sperm Cell: Male sex cell.
  • Egg Cell: Female sex cell.

Structure and Function of Sperm Cells

• Purpose: Transfer male genetic material to the female egg.
• Structure:
  • Head: Contains genetic material and the acrosome.
    • Genetic Material: DNA within the nucleus.
    • Acrosome: Enzymes important for fertilization.
  • Middle Section: Contains mitochondria.
    • Mitochondria: Provide energy to propel the sperm.
    • Quantity: 75-100 large mitochondria, often fused.
  • Tail (Flagellum): Propels the sperm forward.

Structure and Function of Egg Cells

• Size: Significantly larger than sperm, visible to the human eye.
• Structure:
  • Nucleus: Contains female genetic material.
  • Zona Pellucida: Thick layer of glycoproteins that sperm must penetrate.
  • Plasma Membrane: Boundary for genetic material entry.
  • Organelles:
    • Mitochondria: 100,000 - 200,000 present.

Process of Fertilization

• Contact: Sperm meets and binds to the zona pellucida.
  • Acrosomal Reaction: Enzymes from the acrosome digest the zona pellucida.
• Penetration: Sperm head reaches the plasma membrane.
  • Cortical Reaction: Prevents multiple sperm from entering (block to polyspermy).
    • Cortical Granules: Release enzymes to modify zona pellucida, blocking additional sperm.
• Fusion: Plasma membranes of sperm and egg fuse.
  • Genetic Material Transfer: Male genetic material enters the egg.

Mitochondrial Contribution

• Mitochondrial DNA: Mostly contributed by the female.
  • Reason: Large number of mitochondria in the egg compared to sperm.

Important Concepts

• Polyspermy Block: Ensures only one sperm fertilizes the egg.
• Mitochondrial DNA: Predominantly maternal origin due to statistical advantage.