Mendelian and non-Mendelian factors affecting the cytochrome system in Neurospora crassa

Abstract

It was reported recently that the characteristics of a slow-growing strain, called poky, are inherited maternally.(1) This observation has focused attention on strains which grow slowly on complete medium and which have long been known to appear very frequently in material examined in order to detect nutritional mutants of Neurospora. An indication of the frequency of their appearance can be obtained from some figures taken from the data of Beadle and Tatum.(2) Among 8795 ascospores isolated from irradiated material during their study by one of the present authors (M.B.M.), 7049 germinated. Of these, 54 gave rise to strains having easily diagnosed requirements for components present in the complete medium used and, therefore, represented the class of nutritional mutants sought. A much greater number, 489, were distinguishable from wild type because of their slower growth on complete medium. Of these 159 did not grow sufficiently to allow their being tested. The remaining 330 were discarded, either because they grew too rapidly on minimal medium, or because they did not give a well-defined response to the growth-factor mixtures present in the complete medium. Similar figures have been reported by Lein, Mitchell, and Houlahan(3) in a description of a variation in the method of Beadle and Tatum.(2)