Lecture Notes: Spermatogenesis

Introduction to Spermatogenesis

• Process of producing haploid sperm cells.
• Begins with spermatogonia (stem cells).

Mitosis in Spermatogenesis

• Spermatogonia undergo mitosis to ensure a reserve of stem cells.
  • Mitosis involves doubling DNA from 23 to 46 chromosomes, then dividing into two identical cells with 23 pairs of chromosomes.

Meiosis and Spermatogenesis

• Spermatogenesis involves formation of sperm from spermatogonia.
• Primary spermatocytes undergo meiosis I, forming haploid secondary spermatocytes.
  • Diploid: 23 pairs of chromosomes.
  • Haploid: 23 chromosomes.
• Meiosis II results in haploid spermatids.
  • Spermatids are connected by cytoplasmic bridges.
  • Key stages:
    • Spermiogenesis: Maturation of spermatids into sperm.
    • Spermiation: Release of sperm from connection to Sertoli cells.

Stages and Types of Cells

• Spermatogonia: Stem cells, diploid (46 chromosomes).
• Primary Spermatocytes: Diploid.
• Secondary Spermatocytes: Haploid, after meiosis I.
• Spermatids to Sperm Cells: Both haploid, after meiosis II.

Chromosomal Details in Humans

• Somatic Cells: All body cells except sperm and egg, diploid (23 pairs).
  • Homologous chromosomes from mother and father.
• Autosomes: 22 pairs, non-sex chromosomes.
• Sex Chromosomes: 1 pair (23rd pair), X or Y.
  • Females: XX
  • Males: XY (X from mother, Y from father).

Genetic Implications

• Y chromosome: Small, confirms maleness.
• X chromosome: Larger, carries various genes.
  • Males often have X-linked chromosomal abnormalities, e.g., red-green color blindness, male pattern baldness, muscular dystrophy, hemophilia.
• Default development is female; Y chromosome triggers male differentiation.

Gametes and Genetic Variation

• Gametes: Haploid cells (sperm and egg).
  • Sperm can have X or Y, eggs have X.
  • Single set of chromosomes (23 each).
• Produced by meiosis for genetic diversity.
  • Mitosis creates identical cell pairs; meiosis creates diverse cells.
  • Encourages genetic recombination.