Escape from repeat-induced point mutation of a gene-sized duplication in Neurospora crassa crosses that are heterozygous for a larger chromosome segment duplication

In Neurospora crassa the ability of an ectopic gene-sized duplication to in duce repeat-indued point mutation (IP) in its target gene was suppressed in crosses that were heterozygous for another larger chromosome segment dupli cation. Specifically, the frequency of RIP in the erg-3 gene due to a 1.3-k b duplication was reduced if the chromosome segment duplications Dp (IIIR > [I:II]),AR17, Dp(VIR > IIIR) OY329, or Dp(IVR > VII) S1229 were present in either the same or the other parental nucleus of the premeiotic dikaryon. We suggest that the larger duplications act as sinks to titrate the RIF mac hinery away from the smaller duplication. In contrast, RIP efficiency was r elatively unaffected in comparably unproductive interspecies crosses with N . intermedia and N. tetrasperma. These findings offer a novel explanation f or the observed persistence of the transposable element Tad in only a subse t of Neurospora strains.