Why dikaryotic phase is found in fungi?

Different types of fungus have different methods of reproduction. The unicellular yeasts reproduce only mitotically, while other fungi, such as mushrooms, have much more complex life cycles involving three distinct phases. These include diploid and haploid phases, like plants, but also a completely different phase: the dikaryotic phase, where two haploid nuclei of different types are present in each cell. A mature mycelium, including the fruiting bodies, is in the dikaryotic phase. Mushrooms, the reproductive structures of an underground mycelium, contain specialized cells on the underside of the cap that produce diploid zygotes through fusion of the two haploid nuclei in each cell; these zygotes are the only diploid phase of the life cycle. Immediately, each zygote undergoes meiosis to produce four haploid spores which are then released from the mushroom. Each of the spores in a mushroom will have one of two mating types, because in the original mycelium, each cell contained a nucleus of each type. The spores are carried, by wind, water, or animals, away from the original mycelium, and some will land on moist food sources, where they can germinate and begin to divide mitotically into haploid mycelia of a discrete mating type. Eventually, two nearby mycelia of different mating types will meet each other and join together, with their cells fusing but the nuclei remaining discrete. This is the beginning of the dikaryotic stage; the mycelium will soon grow reproductive structures and the life cycle begins again.

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