Dikaryon

A dikaryon is a fungal cell or mycelium in which two genetically distinct haploid nuclei share the same cytoplasm. It arises after plasmogamy, the fusion of compatible hyphal cytoplasm, while the paired nuclei remain separate and do not immediately fuse (karyogamy is delayed).

The dikaryotic condition is most prominently described in the Basidiomycota and in some Ascomycota. In basidiomycetes, the fusion of hyphae from compatible mating types produces dikaryotic hyphae that grow and form fruiting bodies, such as mushrooms; each cell in these hyphae commonly contains two distinct nuclei that divide without fusing. Clamp connections are a morphological feature often associated with maintaining the dikaryon during cell division.

Nuclear fusion (karyogamy) occurs later, typically within specialized structures such as basidia or asci, producing a diploid nucleus that then undergoes meiosis to generate haploid spores. Thus, the dikaryon represents a temporary, specialized nuclear state that enables sexual recombination and genetic diversity.

While the term dikaryon is sometimes used specifically for cells with two distinct nuclei per cell, some fungi can harbor cells with more than two nuclei. In general, the dikaryon is a subset of the broader term heterokaryon, which refers to any cell containing two or more genetically different nuclei.