A system for the screening of reversions in an arginine-dependent strain of Neurospora has been developed.
Reversion resulted from any one of three events:
(a) Back mutation of the original arg gene.
(b) Forward mutation at the pyr locus. This has the pleiotropic effect of suppressing arg while determining a pyrimidine requirement. Interaction with the unmutated nuclei of the same conidium permits growth on minimal medium.
(c) Forward mutation at the pyr locus to alleles of intermediate activity. These alleles suppress arg, but do not create a pyrimidine requirement.