Zoology · Ch 2 — Human Reproduction
Gametogenesis
Gametogenesis
Gametogenesis is the process by which the primary sex organs produce gametes — sperm in the testis, ova in the ovary — in every sexually reproducing organism, and meiosis is the single most important mechanism driving it, since it is what reduces the diploid chromosome number of a germ cell down to the haploid number carried by a mature gamete. Although spermatogenesis and oogenesis share this same underlying meiotic machinery, they differ sharply in their timing, in how many functional gametes each starting cell yields, and in when they are completed — differences that the following sections trace out s …
What this figure shows. A single composite flow chart placing spermatogenesis and oogenesis side by side for direct comparison. The spermatogenesis arm runs spermatogonia, through mitotic division, into a primary spermatocyte, through meiosis I into two secondary spermatocytes, through meiosis II into four spermatids, which become spermatozoa via spermiogenesis. The oogenesis arm, marked across foetal life and adult reproductive life, runs oogonia, through mitotic division, into a primary oocyte, which completes meiosis I only just prior to ovulation to give a secondary oocyte plus a first polar body, and completes meiosis II only on fertilisation to give the ovum plus a second polar body …