39. Gametogenesis. Spermatogenesis. Oogenesis.

-Process of formation of gametes (sex cells) from spermatogonia and oogonia (immature sex cells) -In animals and humans, it takes place in specialised organs (gonads) -Spermatogenesis (formation of sperm) occurs in epithelium of wall of convoluted tubules of testes -Oogenesis (formation of eggs) takes place in follicles in ovaries under action of follicle-stimulating and luteinizing hormones

-Start from diploid precursor cells (spermatogonia and oogania) -These cells, after a period of mitotic division, enter meiosis, becoming haploid cells.

Oogenesis: -Growth: Oocytes grow large, surrounded by a follicle. -Meiosis: Begins embryonically, stops twice (prophase I, metaphase II), ends at fertilization. -Accumulation: Ribosomes, yolk, glycogen, lipids, mRNA. -Function: From puberty to menopause. Spermatogenesis: -Reduction: Spermatocytes shrink post-meiosis. -Structures: –Compacted nucleus. –Acrosome (attaches to egg). –Tail (axoneme) with mitochondria. -Meiosis: Begins at puberty, continuous until old age.

Process: Starts at puberty, continuous until old age. Location: Epithelium of testicular tubules (~300 m in length). Spermatogonia Types: -Type Ad: Dark, stem cells, produce type Ap. -Type Ap: Pale, produce type B. -Type B: Round nuclei, produce primary spermatocytes. Primary Spermatocytes: Diploid (46 chromosomes), undergo meiosis I to form secondary spermatocytes. Secondary Spermatocytes: Haploid (23 chromosomes), undergo meiosis II to form spermatids. Spermatids: Result: 4 haploid spermatids from 1 spermatogonium. Spermiogenesis: Formation of mature sperm structures: condensed nucleus, acrosome, axoneme, and mitochondria.

1.Primordial Cells: Migrate to gonads, become oogonia. 2.Proliferation: Oogonia divide by mitosis until 11-12 weeks of embryo development. 3.Primary Oocytes: Enter meiosis I, stop at diplotene of prophase I until puberty. 4.Ooplasmic Segregation: Continues despite meiosis pause. 5.Oocyte Maturation: Begins at puberty, hormone-stimulated. -Telophase I: Asymmetric cytoplasm division forms large secondary oocyte and small polar body. -Meiosis II: Starts, stops at metaphase II before ovulation. -Follicle Maturation: Most die; ~400-450 mature out of ~400,000. 6. Ovulation: Mature egg leaves ovary, completes meiosis II if fertilized.