Gamete

Gamete is a haploid sex cell that participates in sexual reproduction. In animals, the two main types are sperm, the male gametes, and oocytes (eggs), the female gametes. Gametes arise from germ cells through gametogenesis, most commonly meiosis, which reduces the chromosome number from diploid to haploid and generates genetic variation through recombination and independent assortment. Spermatogenesis occurs in the testes and produces motile sperm, while oogenesis occurs in the ovaries and yields relatively large, nutrient-rich egg cells, often produced in a limited number.

In plants, fungi, and algae the term covers analogous haploid reproductive cells as well. In seed plants, male gametophytes are pollen grains and female gametophytes develop within ovules; in many algae and bryophytes a variety of isogametes or oogamous gametes exist.

Fertilization is the fusion of two gametes to form a diploid zygote, restoring the species’ chromosome number and initiating embryonic development. The timing and location of fertilization vary: external fertilization in many aquatic organisms and internal fertilization in most terrestrial animals, including humans. Gametogenesis and fertilization are central to sexual reproduction and contribute to genetic diversity.

Clinical and practical aspects include assisted reproduction technologies that manipulate gametes, such as insemination, in vitro fertilization, and gamete donation, as well as screening for chromosomal abnormalities. In plants, the alternation of generations describes the cycle between haploid gametophyte and diploid sporophyte stages.