There are 4 genotypic classes of pairings basic to the tetrapolar, or bifactorial, mating system of the Basidiomycete Schizophyllum commune. One class has a complex phenotype termed “common‐A heterokaryosis.” Analysis shows a high nuclear ratio to be characteristic of this heterokaryon. Selection of the majority type is independent of input nuclear ratio. The common‐A phenotype is interpreted from old and new data to include several major traits: (1) absence of nuclear pairing and conjugate division; (2) extreme variation of nuclear ratio; (3) absence of clamp connections; (4) depression of growth, as measured by rate and final amount dry weight; and (5) usual absence of fruiting. The absence of non‐allelic complementation, previously described as part of the phenotype, has been discounted by new results. The possibility of a quantitative effect of incompatibility remains undecided.
S"lIDER, P. J. (U. California, Berkeley.) Estimation of nuclear ratios directly from heterokaryotic mycelia in Schizophyllum. Amer. Jour. Bot. 50 (3): 255-262. Illus. 1963.-The principles used to analyze nuclear ratios with macerated mycelium are similar in part to those of classic methods utilizing spore suspensions, but some distinctive features are evident in the present method. It is simple, adapted particularly for analyzing highly disparate ratios, and probably suitable for the simultaneous comparison of ratios in mycelium and spores. The technique can be combined with others, as described, to devise a test suggesting whether random or non-random spatial distributions of nuclei exist in heterokaryons with disparate ratios. Direct analysis, as described and evaluated here, was used in a study reported in a companion paper, and numerous applications in fungi seem probable.
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