Pleiotropic and differential phenotypic expression of two sn (snowflake) mutant alleles of Neurospora crassa: analysis in homokaryotic and heterokaryotic cells.

Mutations sn (snowflake) JL301 and C136, in the centromere region of linkage group I in Neurospora crassa, are at 0.6-3.0 map units to the left of the os-4 locus. Strains carrying snJL301 produce very short aerial hyphae and only arthroconidia, and do not grow in high salt media. snC136 strains produce aerial hyphae, with abnormally large and rounded blastoconidia, at the top of the agar slant cultures, and revert to wild-type growth in high salt media. Studies with forced primary heterokaryons indicate that snJL301 is recessive while snC136 is a semi-dominant and gene-dose dependent allele, with respect to the wild-type. Taken together the results show that: (1) the sn mutations are allelic with a differential pleiotropic phenotype, and (2) snC136 may code for a partially functioning gene product while snJL301 appears to be a null allele.