Gametogenesis

Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of diploid gametocytes into various gametes, or by mitosis. For example, plants produce gametes through mitosis in gametophytes. The gametophytes grow from haploid spores after sporic meiosis. The existence of a multicellular, haploid phase in the life cycle between meiosis and gametogenesis is also referred to as alternation of generations.

It is the biological process of gametogenesis during which cells that are haploid or diploid divide to create other cells. It can take place either through mitotic or meiotic division of diploid gametocytes into different cells depending on an organism's biological life cycle. For instance, gametophytes in plants undergo mitosis to produce gametes. Both male and female have different forms.

Animals produce gametes directly through meiosis from diploid mother cells in organs called gonads (testis in males and ovaries in females). In mammalian germ cell development, sexually dimorphic gametes differentiate into primordial germ cells from pluripotent cells during initial mammalian development. Males and females of a species that reproduce sexually have different forms of gametogenesis:

However, before turning into gametogonia, the embryonic development of gametes is the same in males and females.

Gametogonia are usually seen as the initial stage of gametogenesis. However, gametogonia are themselves successors of primordial germ cells (PGCs) from the dorsal endoderm of the yolk sac migrate along the hindgut to the genital ridge. They multiply by mitosis, and, once they have reached the genital ridge in the late embryonic stage, are referred to as gametogonia. Once the germ cells have developed into gametogonia, they are no longer the same between males and females.

From gametogonia, male and female gametes develop differently – males by spermatogenesis and females by oogenesis. However, by convention, the following pattern is common for both:

In vitro gametogenesis (IVG) is the technique of developing in vitro generated gametes, i.e., "the generation of eggs and sperm from pluripotent stem cells in a culture dish." This technique is currently feasible in mice and will likely have future success in humans and nonhuman primates. It allows scientists to create sperm and egg cells by reprogramming adult cells. This way, they could grow embryos in a laboratory. Even though it is a promising technique for fighting disease, it raises several ethical problems.

Fungi, algae, and primitive plants form specialized haploid structures called gametangia, where gametes are produced through mitosis. In some fungi, such as the Zygomycota, the gametangia are single cells, situated on the ends of hyphae, which act as gametes by fusing into a zygote. More typically, gametangia are multicellular structures that differentiate into male and female organs: