Frequency of spontaneous and induced recessive mutations in a diploid strain of Aspergillus nidulans.

The spontaneous and UV-induced frequencies of recessive mutations have been studied in a diploid strain of Aspergillus nidulans, by the p-fluoro-phenylalanine (FPA) and 8-azaguanine (8-AZA) resistance tests, on either resting or germinating conidia. Observed frequencies are in the order of magnitude of those expected, which have been calculated considering the observed mutation frequencies in the haploid strain as well as the mitotic recombination frequencies. We also review some papers which claim to have found higher rates of recessive mutations in mammalian cell lines; in some cases no really higher rates are evident and the authors' conclusions often rest on misinterpretation of their own data.