Understanding the Barriers to Interspecific Hybridization in Neurospora
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Crosses between two species of Neurospora are typically sterile and result in the production of non-viable or few viable ascospores. It is unclear what prevents successful sexual reproduction and the viability of hybrid progeny, given that most species of Neurospora share high levels of genetic and phenotypic similarity. It has been hypothesized that genome defense and integrity checkpoints play a critical role in preventing successful crosses between two different species. In particular, we hypothesized that either meiotic silencing, DNA methylation, and/or DNA mismatch repair, or a combination of the above might pose a barrier to interspecific reproduction. To test this hypothesis, we have selected the species Neurospora crassa and Neurospora tetrasperma. We used loss-of-function mutations or deletions in key genes for meiotic silencing, DNA methylation, and/or DNA mismatch repair in Neurospora crassa strains and, using spore quantification assays, examined the effect of such mutations in crosses with Neurospora tetrasperma. A significant increase in ascospore production was only shown in crosses containing a deletion of the Sad-1 gene in the N. crassa strain. In iv contrast, no increase in ascospore production was observed by either deletion or mutagenesis of the Sms-4 gene. Progeny obtained from crosses containing the deletion in Sad-1 were germinated and analyzed based on genetic and phenotypic characteristic. Most of the progeny were classified as hybrid and inherited Linkage Group I containing the deletion of Sad-1 from N. crassa. Our results suggest that meiotic silencing does not have a significant contribution to reproductive isolation; rather Sad-1 contributes directly to reproductive isolation at the meiotic stage.
DNA mismatch repair
Gajjar, Sameer 1990- (2012). Understanding the Barriers to Interspecific Hybridization in Neurospora. Honors and Undergraduate Research. Available electronically from