ADDITIVE ACTION OF PARTIAL HETEROKARYON INCOMPATIBILITY (PARTIAL-HET)GENES IN ASPERGILLUS-NIDULANS

We have observed partial heterokaryon-incompatibility reactions in com binations of field isolates of A. nidulans. We have demonstrated that partial heterokaryon incompatibility is genetically controlled by gene s (partial-het genes) operating in the same manner as the previously-d escribed het genes. Our results also reveal that partial-het genes can act additively in causing heterokaryon incompatibility and that parti al heterokaryon incompatibility is not a barrier to the horizontal tra nsfer of a mitochondrial marker. These results add to the growing body of evidence that vegetative-incompatibility reactions are not an abso lute barrier to horizontal gene flow.