Spermatogenesis

Primordial germ cells (2n) present in the germinal epithelium of the seminiferous tubules undergo repeated mitotic divisions, producing a large population of spermatogonia (2n), each containing 46 chromosomes.

• Type A cells - continue dividing (self-renewing reserve pool)
• Type B cells - stop dividing, move towards the lumen, and enter the Growth Phase
• Type B cells are also called sperm mother cells or spermatogonia precursors

Type B spermatogonia absorb large quantities of nutrients and grow considerably in size - approximately doubling in volume. These enlarged cells are now designated Primary Spermatocytes (2n). DNA replication occurs during this phase in preparation for meiosis.

Phase III: Maturation Phase (Meiotic Divisions)

This is the critical phase where chromosome number is halved. It comprises two sub-divisions:

Meiosis I - First Maturation (Reduction) Division

• Each Primary Spermatocyte (2n, 46 chromosomes) undergoes the first meiotic (reduction) division
• Produces two Secondary Spermatocytes — each haploid (n, 23 chromosomes)
• This is where ploidy reduction (2n → n) occurs

Meiosis II - Second Maturation Division

• Each Secondary Spermatocyte (n) undergoes the second meiotic division
• Produces four equal, haploid spermatids (n, 23 chromosomes) - all equal in size
• Spermatids are round, non-motile, and non-functional at this stage