Chromosome segment duplications in Neurospora crassa : barren crosses beget fertile science

Studies on Neurospora chromosome segment duplications ( Dp s) performed since the publication of Perkins's comprehensive review in 1997 form the focus of this article. We present a brief summary of Perkins's seminal work on chromosome rearrangements, specifically, the identification of insertional and quasiterminal translocations that can segregate Dp progeny when crossed with normal sequence strains ( i.e ., T  ×  N ). We describe the genome defense process called meiotic silencing by unpaired DNA that renders Dp ‐heterozygous crosses ( i.e ., Dp  ×  N ) barren, which provides a basis for identifying Dp s, and discuss whether other processes also might contribute to the barren phenotype of Dp  ×  N and Dp  ×  Dp crosses. We then turn to studies suggesting that large Dp s ( i.e ., >300 kbp) can allow smaller gene‐sized duplications to escape another genome defense process called repeat‐induced point mutation (RIP), possibly by titration of the RIP machinery. Finally, we assess whether in natural populations dominant RIP suppressor Dp s provide an “RIP‐free” niche for evolution of new genes following the duplication of existing genes.