MUTATIONS AFFECTING HETEROKARYOSIS IN SCHIZOPHYLLUM COMMUNE

Mutations that affect the basic characteristics of heterokaryons of S. commune occur spontaneously and are preferentially selected in the common-A heterokaryon and in its homokaryotic mimics, strains carrying a mutated B factor or strains disomic for heteroallelic B factors. Nine independent mutations were compared: all segregate independently of A and B incompatibility factors, and at least 3 distinct loci, of which 2 are linked, are involved. None of the mutations is phenotypically expressed in the homokaryon or in the common-AB heterokaryon. All 9 mutations increase vegetative vigor of the common-A the effects of all the mutations are additive in both heteroallelic and homoallelic combinations. At least 1 type-II mutation also affects nuclear distribution in common-B heterokaryons. Type-II mutations appear to reduce common-A, common-B, and compatible heterokaryons to a single type unlike any of the normal heterokaryons. Pseudoclamping often persists for extended periods in modified homokaryons isolated from modified heterokaryons. Several cases of somatic recombination have been observed among components of modified heterokaryons.