Abstract

SUMMARY: Roper’s technique for the production in filamentous fungi of strains with heterozygous diploid nuclei in their hyphae (Roper, 1952) has been applied successfully to Aspergillus niger, in which a sexual cycle does not occur. The diploids, heterozygous for known markers, give origin to new strains, most still diploid, homozygous for some or all of the markers and therefore associating or recombining in all possible ways the properties of the two strains from which the diploid was formed. Genetic recombination has thus been achieved in a filamentous fungus without a normal sexual cycle. Imperfect fungi are now open to genetic investigation. Deliberate ‘breeding’ of strains has become a practical proposition in industrial fermentations based on these fungi.