Gametogenesis is the process by which gametes are produced in organisms endowed with sexual reproduction. In animals, gametogenesis occurs in the gonads, organs that also produce sex hormones, which determine the characteristics that differentiate males from females.
The fundamental event of gametogenesis is meiosis, which halves the amount of cell chromosomes, resulting in haploid cells. In fertilization, the fusion of two haploid gametes reconstitutes the characteristic diploid number of each species.
In some rare cases, meiosis does not occur during gamete formation. A well-known example is that of bees: if an egg is not fertilized by any sperm, it will develop into consecutive mitoses, resulting in an embryo in which all cells are haploid. This haploid embryo will form a male individual.
The development of a gamete without fertilization is called parthenogenesis. If the egg is fertilized, the embryo 2n will give rise to a female.
Generally speaking, male gametogenesis (or spermatogenesis) and female gametogenesis (ovogenesis or ovulogenesis) follow the same steps. We will study each one below.