Nuclear and extranuclear inheritance of oligomycin resistance in Aspergillus nidulans

Summary A number of spontaneously-occurring, stable oligomycin-resistant mutants have been isolated in Aspergillus nidulans. Genetic characterisation showed that while most of the mutants examined were nuclear, one mutant was extranuclear as judged by several criteria. While the nuclear mutants showed no abnormalities on drug-free medium, the extranuclear mutant exhibited impaired growth ability. This character never segregated from the oligomycin-resistance character in any of the genetic experiments carried out, and appeared to be a secondary effect of the same mutation. The extranuclear genetic element coding for the oligomycin-resistance character was unable to co-exist in a stable fashion within the same mycelium as the wild type element, and they tended to segregate into sectors consisting almost wholly of one type or the other. The nuclear mutants showed incomplete dominance in heterozygous diploids, segregating fully resistant homozygous areas. All nuclear mutants mapped on linkage group VII.