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Gametogenesis – spermatogenesis and oogenesis side by side

BiologyHuman & Animal PhysiologyAges 16–17

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Use with my class

A side-by-side timeline of spermatogenesis and oogenesis: spermatogonium, primary and secondary spermatocytes, spermatids and sperm, against oogonium, primary oocyte arrested in prophase I from before birth, secondary oocyte and first polar body at ovulation, and ovum and second polar body only after a sperm enters, ending in the zygote. Chromosome number, ploidy and DNA content are shown at every stage, with the roles of FSH, LH and testosterone. Virtual T.S. slides of a seminiferous tubule and an ovary with follicle stages link each cell to its place in the gonad.

Lesson: Gametogenesis: spermatogenesis and oogenesis; microscopic structure of the testis and ovary

What it shows

Gametes form by meiosis, so each sperm and egg carries 23 chromosomes and fertilisation restores 46. In the testis, spermatogenesis runs from puberty onwards and one primary spermatocyte gives four sperm. In the ovary, oogenesis starts before birth: primary oocytes pause in meiosis I for years, and each cycle usually only one completes it. Unequal divisions give one large ovum and small polar bodies, and meiosis II finishes only after a sperm enters. The diagrams are schematic: cells are drawn with 2n = 4 chromosomes to show the steps, and crossing over is not shown.

How to use

On Timeline, press Run or Step, or drag Stage, and read the testis and ovary rows; the table fills in stage by stage. Tick Hormones to see the hormone controls. On Testis section and Ovary section, choose Study and tap a cell or a numbered marker, or choose Spot test, name the cell at the red arrow, choose its Ploidy and press Check. Answer Task 2 and press Check.

Parameters you can change

  • Screen Timeline, Testis section, Ovary section
  • Stage 1–6
  • Show hormones
  • Mode Study, Spot test

Questions to explore

  1. Why does one primary oocyte give only one ovum while one primary spermatocyte gives four sperm?
  2. At which stages are the cells haploid, and when does the DNA content per cell halve?
  3. How do LH and FSH act on the Leydig and Sertoli cells to control sperm production?

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