Dikaryon

A dikaryon (from the Greek di- meaning "two" and karyon meaning "nucleus") is a cell or fungal hypha in which two genetically distinct nuclei coexist and divide without nuclear fusion. The two nuclei, derived from different parent cells, remain separate within the same cytoplasm. This condition is represented as n+n, signifying two haploid (n) nuclei.

The dikaryotic state is a characteristic feature of certain fungi, particularly in the Ascomycota and Basidiomycota divisions, during a specific phase of their life cycle. It typically arises following plasmogamy, the fusion of two protoplasts (cell contents), which brings the two haploid nuclei together into a single cell. Karyogamy, the fusion of these nuclei to form a diploid nucleus, is delayed.

The dikaryotic phase can be relatively short-lived or quite extended, depending on the fungal species. In Basidiomycetes, the dikaryotic mycelium is often the dominant, long-lived phase. The coordinated division of the two nuclei within the dikaryon is essential for maintaining the n+n state and ensuring that each daughter cell receives a complete set of genetic information from both parental nuclei. This coordination is facilitated by specialized structures, such as clamp connections in Basidiomycetes, which help to ensure proper nuclear segregation during cell division.

The dikaryotic stage allows for genetic exchange and recombination without immediate karyogamy. This can lead to increased genetic diversity within the fungal population and provide opportunities for adaptation to changing environmental conditions. The dikaryon ultimately undergoes karyogamy to form a diploid nucleus, which then typically undergoes meiosis to produce haploid spores, completing the life cycle.