The processes of spermatogenesis and oogenesis in humans are similar in that they both:

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11ecba2d_1021_11c1_a3bf_3b24ce41d5c3_MD0008_00 In humans, the generation of reproductive cells (gametes) occurs in reproductive glands known as the gonads. Before puberty, stem cells called spermatogonia undergo continuous mitotic divisions within the male gonads (ie, testes) to yield identical daughter cells. At puberty, spermatogenesis (sperm production) begins and continues throughout the male's life. In spermatogenesis, some of the daughter cells produced from mitotic divisions of spermatogonia become primary spermatocytes. Primary spermatocytes then become mature sperm via meiosis, a process involving two rounds of cell division known as meiosis I and II. A primary spermatocyte that undergoes meiosis I yields two identical haploid cells labeled secondary spermatocytes. Each secondary spermatocyte then undergoes meiosis II to produce four identical haploid spermatids that develop into mature sperm. In contrast to spermatogenesis, oogenesis (oocyte production) begins before birth, not at puberty, in the female gonads (ie, ovaries) (Choice A). In the female embryo, oogonia (stem cells) undergo mitosis to produce primary oocytes. Each primary oocyte is surrounded by a saclike structure called a follicle. Although they must also undergo meiosis to mature, primary oocytes begin meiosis I but become arrested at prophase I until puberty. At puberty, one primary oocyte is selected during each menstrual cycle to complete meiosis I. Unlike in spermatogenesis, meiosis I in oogenesis yields two haploid cells of unequal size, the larger one being a secondary oocyte and the smaller one being a polar body that eventually degenerates (Choice C). The secondary oocyte then begins meiosis II but is arrested at metaphase II. The secondary oocyte completes meiosis II and fully matures only if fertilization occurs. To be fertilized, the secondary oocyte must be released during the ovulation phase of the menstrual cycle. During this phase, the follicle ruptures from the ovary and the oocyte enters the fallopian tube to be fertilized by mature sperm. (Choice D) Oogenesis begins before birth but ceases in older women when ovarian production of female sex hormones declines (ie, menopause). In contrast, spermatogenesis begins at puberty and continues throughout the male's life. Neither process occurs continuously throughout an organism's entire life-span. Educational objective: Both spermatogenesis and oogenesis involve cells that undergo meiosis I and II. However, oogenesis in females begins in the female embryo and ends at menopause, whereas spermatogenesis in males does not begin until puberty and continues throughout a male's life.

The Processes of Spermatogenesis and Oogenesis in Humans Are Similar