MITOCHONDRIAL INHERITANCE IN ASPERGILLUS-NIDULANS

Mitochondrial chloramphenicol and oligomycin resistance mutations were used to investigate mitochondrial inheritance in A. nidulans. Mitocho ndrial RFLPs could not be used to distinguish between paternal and mat ernal mitochondria because none were detected in the 54 isolates inves tigated. Several thousand ascospores from each of 111 hybrid cleistoth ecia from 21 different crosses between 7 heterokaryon incompatible iso lates were tested for biparental inheritance. All mitochondrial inheri tance was strictly uniparental. Not one instance of paternal inheritan ce of mitochondria was observed. The implications of our results for t he theory that uniparental inheritance evolved to avoid cytoplasmic co nflict are discussed. Possible explanations for the maintenance of str ict uniparental inheritance of mitochondria in an inbreeding homothall ic organism are suggested. The chloramphenicol resistance marker was i nherited preferentially to the oligomycin resistance marker probably d ue to the inhibited energy production of mitochondria with the oligomy cin resistance mutation. The maternal parent was determined for 93 hyb rid cleistothecia from 17 crosses between 7 different strains. Contrar y to previous reports A. nidulans strains functioned as both maternal and paternal parent in most crosses.