RPM points to a couple great papers on the genetics of speciation in Drosophila and mouse. The first is particularly interesting–the gene underlying hybrid incompatibility is also involved in meiotic drive.
What’s fun about these sorts of studies is that one can almost start to reconstruct the sequence of population genetic events leading to speciation–like all alleles, one that leads to hybrid infertility has to pass through a phase in which it segregates in the population. This is counterintuitive, of course–any allele causing infertility in some fraction of offspring should be deleterious. One possibility is that divergence at these genes is due to differential selection, and this new paper raises the possibility that sometimes this selection might not be due to external selection pressures, but rather to intragenomic conflict.