A fungal mycelium that contains two or more haploid nuclei per cell.
In most fungi during the plasmogamy, the haploid nuclei contributed by each parent do not fuseright away. Instead parts of the fused mycelium contain coexisting, genetically different nucli.
- Such a mycelium is said to be a heterokaryon
- (meaning "different nuclei").
In some species, the different nuclei may even exchange chromosomes and genes in a process similar to crossing over. In other species, the haploid nuclei pair off two to a cell, one from each parent (known as dikaryotic - meaning two nuclei).