Sexual Reproduction in Animals: Gametogenesis

Sexual reproduction in animals involves the formation and fusion of male and female gametes. The process of gamete formation is called gametogenesis.

Gametogenesis: Spermatogenesis and Oogenesis

Spermatogenesis is the process of sperm production in the testes.

  • Spermatogonia: Diploid cells that undergo mitosis to produce more spermatogonia.

  • Primary Spermatocyte: Some spermatogonia differentiate into primary spermatocytes.

  • Meiosis I: Primary spermatocytes undergo meiosis I to produce two haploid secondary spermatocytes.

  • Meiosis II: Secondary spermatocytes undergo meiosis II to produce four haploid spermatids.

  • Spermiogenesis: Spermatids undergo a series of changes to develop into mature sperm cells, acquiring a head, midpiece, and tail.

Oogenesis is the process of egg cell (ovum) production in the ovaries.

  • Oogonia: Diploid cells that undergo mitosis to produce more oogonia.

  • Primary Oocyte: Some oogonia differentiate into primary oocytes.

  • Meiosis I: Primary oocytes undergo meiosis I, producing a secondary oocyte and a smaller polar body.

  • Meiosis II: The secondary oocyte can undergo meiosis II to produce a mature egg cell and a second polar body.

Key Points:

  • Gamete Formation: Both spermatogenesis and oogenesis involve meiosis, which reduces the chromosome number from diploid to haploid.

  • Gamete Structure: Sperm cells are flagellated and motile, while egg cells are large and non-motile.

  • Polar Bodies: During oogenesis, polar bodies are formed as a result of unequal cytoplasmic division.

  • Gonads: Testes and ovaries are the specialized organs where gametogenesis occurs.

Sexual reproduction ensures genetic diversity in offspring, which is essential for the survival and evolution of species.