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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.
Antheridia and archegonia occur on different gametophytes, which are then called dioicous. The moss Mnium hornum has the gametophyte as the dominant generation. It is dioicous: male plants produce only antheridia in terminal rosettes, female plants produce only archegonia in the form of stalked capsules. [26] Seed plant gametophytes are also ...
Mitosis does occur, but no cell divisions are ever made. [13] This results in the mature female gametophyte in some Gnetophyta having many free nuclei in one cell. Once mature, this single celled gametophyte is 90% smaller than the female gametophytes in other gymnosperm orders. [14]
These spores then germinate and divide by mitosis to form a haploid multicellular phase, the gametophyte, which produces gametes directly by mitosis. This type of life cycle, involving alternation between two multicellular phases, the sexual haploid gametophyte and asexual diploid sporophyte, is known as alternation of generations .
These undergo mitosis to form male gametophytes, each of which contains two haploid cells. Meanwhile, the ovules produce megaspores by meiosis, further division of these form the female gametophytes, which are very strongly reduced, each consisting only of a few cells, one of which is the egg.
The microspore divides by mitosis producing two cells. The first of the cells (the generative cell) is small and is formed inside the second larger cell (the tube cell). The members of each part of the microspores separate from each other. A double-layered wall then develops around each microspore.
The sporophyte creates spores via meiosis which also then divide mitotically producing haploid individuals called gametophytes. The gametophytes produce gametes via mitosis. In some plants the gametophyte is not only small-sized but also short-lived; in other plants and many algae, the gametophyte is the "dominant" stage of the life cycle. [19]
The mitosis process in the cells of eukaryotic organisms follows a similar pattern, but with variations in three main details. "Closed" and "open" mitosis can be distinguished on the basis of nuclear envelope remaining intact or breaking down. An intermediate form with partial degradation of the nuclear envelope is called "semiopen" mitosis.