Breaking a species barrier by enabling hybrid recombination

Hybrid sterility maintains reproductive isolation between species by preventing them from exchanging genetic material. Anti-recombination can contribute to hybrid sterility when different species’ chromosome sequences are too diverged to cross-over efficiently during hybrid meiosis, resulting in chromosome mis-segregation and aneuploidy. The genome sequences of the yeasts Saccharomyces cerevisiae and Saccharomyces paradoxus have diverged by about 12% and their hybrids are sexually sterile: nearly all of their gametes are aneuploid and inviable. Previous methods to increase hybrid yeast fertility have targetted the anti-recombination machinery, enhancing meiotic crossing over but also having counteracting detrimental effects on gamete viability due to increased mutagenesis and ectopic recombination. Therefore the role of anti-recombination has not been fully revealed, and it is often dismissed as a minor player in speciation. By repressing two genes, SGS1 and MSH2, specifically during me...