Magic with moulds: Meiotic and mitotic crossing over in Neurospora inversions and duplications

摘要

In 1982 Barbara Turner and David Perkins reported an astonishing resu from a cross between two inversion strains of Neurospora crassa [In(OY348) and In(OY323)] they recovered progeny of the normal sequence (Turner and Perkins 1982). If the normal sequence of loci in linkage group I is represented by ABCDEF.GHIJKL, with the dot representing the centromere, the sequence of the inversion In(OY348) can be depicted as ABHG.FEDCIJKL and that of the inversion In(OY323) by ABCDJIHG.FEKL. Note that the two inversions overlap in the sequence HG.FE. Note also that the recovery of the normal sequence from a cross between the two inversions is neither a trivial nor an obvious outcome. The discovery of the RNAi-based gene silencing process called meiotic silencing by unpaired DNA now provides an explanation for how normal sequence strains come to be selected. Meiotic silencing silences genes that are unpaired in meiosis, as well as their homologues, regardless of whether or not the homologues are themselves paired. This gene-silencing phenomenon was discovered in Neurospora (Shiu et al 2001; Shiu and Metzenberg 2002), and detected more recently also in Caenorhabditis and mouse (Lee 2005).