Roncero M I, Zabala C, Cerdá-Olmedo E
Mutat Res. 1984 Feb;125(2):195-204. doi: 10.1016/0027-5107(84)90069-1.
Multinucleate cells, such as the spores of the fungus Phycomyces, are unsuitable for the isolation of recessive mutants. Nuclear killing by N-methyl-N'-nitro-N-nitrosoguanidine (henceforth nitrosoguanidine) eliminates all but one of the nuclei in some of the cells and allows the expression of recessive mutations. Even in the best conditions, only about 35% of the survivors have a single functional nucleus. Functionally uninucleate cells can be positively selected. This involves the exposure to nitrosoguanidine of the spores of a heterokaryon and selection for a recessive marker present in a small fraction of its nuclei. The optimal conditions for nitrosoguanidine mutagenesis in Phycomyces differ from those for bacteria and yeast. Buffer composition and pH are less important than in other organisms. Survival is an exponential function and mutation induction a linear function of the dose of the mutagen (concentration X time). Spore germination leads to an immediate increase in the number of gene copies per cell, thus further hindering the expression of recessive mutations; dominant mutations are then nearly always isolated in heterokaryotic form.
多核细胞，如藻状菌纲真菌的孢子，不适合用于隐性突变体的分离。用N-甲基-N'-硝基-N-亚硝基胍（以下简称亚硝基胍）进行核杀伤可消除部分细胞中除一个核之外的所有核，并使隐性突变得以表达。即使在最佳条件下，也只有约35%的存活者具有单个功能核。功能上单核的细胞可以进行阳性选择。这涉及将异核体的孢子暴露于亚硝基胍，并选择其一小部分核中存在的隐性标记。藻状菌纲中亚硝基胍诱变的最佳条件与细菌和酵母的不同。缓冲液组成和pH值的重要性低于其他生物体。存活率是诱变剂剂量（浓度×时间）的指数函数，而突变诱导是线性函数。孢子萌发会导致每个细胞中基因拷贝数立即增加，从而进一步阻碍隐性突变的表达；显性突变几乎总是以异核体形式分离出来。
