Additive action of partial heterokaryon incompatibility (partial-het) genes in Aspergillus nidulans.

We have observed partial heterokaryon-incompatibility reactions in combinations of field isolates of A. nidulans. We have demonstrated that partial heterokaryon incompatibility is genetically controlled by genes (partial-het genes) operating in the same manner as the previously-described het genes. Our results also reveal that partial-het genes can act additively in causing heterokaryon incompatibility and that partial heterokaryon incompatibility is not a barrier to the horizontal transfer of a mitochondrial marker. These results add to the growing body of evidence that vegetative-incompatibility reactions are not an absolute barrier to horizontal gene flow.