Gametogenesisthe

Gametogenesis is the biological process by which diploid germ cells develop into haploid gametes suitable for sexual reproduction. It includes two related pathways that produce male and female gametes: spermatogenesis and oogenesis. The process both reduces chromosome number by half and introduces genetic variation through pairing and recombination of homologous chromosomes.

In spermatogenesis, which occurs in the testes, the germline cells called spermatogonia give rise to primary spermatocytes. Through meiosis I and II, these cells produce haploid spermatids that undergo maturation into motile spermatozoa. Spermatogenesis begins at puberty and proceeds continuously in many species, yielding millions of sperm daily. The process is supported by Sertoli cells and is regulated by hormones such as follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone.

In oogenesis, which takes place in the ovaries, oogonia develop into primary oocytes during fetal life and enter prophase I of meiosis, where they become arrested until puberty. Each menstrual cycle selects a cohort of follicles; typically one completes meiosis I to form a secondary oocyte and a first polar body. Meiosis II proceeds only if fertilization occurs, producing the ovum and a second polar body. Oogenesis results in a finite supply of gametes and typically a single ovum per cycle in humans, with significant reproductive timing differences across species.

Genetic variation arises from crossing over during meiosis and independent assortment. Abnormalities in gametogenesis can lead to infertility or chromosomal disorders.