The genetic basis for the meiotic disorder of Coprinus congregatus.

A "pale-mushroom" phenotype in the fungus Coprinus congregatus has previously been reported to be caused by a cytoplasmic, infectious agent that inhibits the formation of synaptonemal complexes. After a period of 5 years of successful extraction of infectious material from carrier homokaryons, infectivity has now been lost and even cytoplasmic contact through somatic fusions no longer transmits the pale phenotype. In attempts to obtain new carrier homokaryons, a genetic analysis has been done. This study demonstrates that the pale phenotype in this species is primarily determined by a nuclear gene, symbolized pal (-). The pale phenotype appears predictably when the dikaryon is homoallelic for the pal (-) allele. Homoallelic wild type (pal (+)) and heteroallelic dikaryons display the dark phenotype. The former infectious nature of the pale phenotype and the current anomalous behavior of one homokaryon is discussed in the context that the pale phenotype may involve both a nuclear gene and a cytoplasmic element under some conditions.