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a cell that has two or more nuclei that differ in hereditary (genetic) properties. Heterokaryons are widespread in fungi, in which they arise from the fusion of the hyphae and the passing of the nuclei from one hypha to another. In the heterokaryon the content of nuclei of various types can disguise the biochemical defects inherent in one or another type. Therefore, heterokaryon can be grown on a nutrient medium that is insufficient for every type of nucleus in isolation. If during the fusion of hyphae the cell receives genetically identical nuclei, it is called a homokaryon.