Gametogenesis and Reproductive Anatomy
Core concepts
Gametogenesis begins with primordial germ cells migrating to the gonadal ridge, then diverges: spermatogenesis is continuous from puberty with mitotic amplification, meiosis, and spermiogenesis; oogenesis arrests in prophase I (dictyate) until the LH surge, completing meiosis II only at fertilization. Know the timing of meiotic resumption, polar body extrusion, and the cytoplasmic asymmetries that give the oocyte its stores of mRNA and mitochondria.
Anatomy that examiners test
Trace the male tract (seminiferous tubules → rete testis → efferent ductules → epididymis → vas deferens → ejaculatory duct) and the female tract (ovary → fimbriae → ampulla → isthmus → uterus). The ampullary-isthmic junction matters because it is the usual fertilization site. Understand follicular recruitment, dominance, and the two-cell two-gonadotropin model (theca androgen → granulosa aromatization).
Traps
- Confusing primary versus secondary oocyte arrest points.
- Assuming spermatogenesis is synchronous across a tubule; it is not.
- Mixing up which cells produce inhibin and which respond to FSH.
- Forgetting that the oocyte contributes most cytoplasmic organelles while the sperm contributes the centriole in most species.
Rule of thumb
"Oocyte waits twice, sperm never waits." If a question asks when meiosis II completes, the answer is fertilization (second polar body). If it asks when meiosis I completes, the answer is the LH surge just before ovulation.