heterokaryosis

The occurrence of normally two nuclei of different genotypes in a fungal cell or mycelium. Heterokaryons tend to grow better than their constituent homokaryons. If one type of nucleus possesses a mutation such that it cannot synthesize a particular compound, then this deficiency is overcome by the other type of nucleus, a phenomenon termed *complementation. Heterokaryosis also allows recombination in imperfect and homothallic fungi (see parasexual recombination).