Embryonic Development in Humans: Gametogenesis, Fertilization, Gastrulation and Organogenesis
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Epigenesis vs. preformationism: Aristotle and William Harvey proposed epigenesis, the view that the embryo develops progressively from an undifferentiated, homogeneous mass. Malpighi and other preformationists maintained that a fully formed miniature organism, the homunculus, already existed in the gamete.
Gametogenesis
Spermatogenesis: spermatogonium (mitosis) → primary spermatocyte → meiosis I → secondary spermatocyte → meiosis II → spermatids → spermatozoa (spermiogenesis).
Oogenesis: oogonium (mitosis) → primary oocyte (arrested for a long period) → primordial follicle (puberty, rapid growth) → primary follicle → zona pellucida → secondary follicle → tertiary follicle (Graafian follicle) → second meiotic division... Continue reading "Embryonic Development in Humans: Gametogenesis, Fertilization, Gastrulation and Organogenesis" »