We have also found that, contrary to the faster-X theory, genes on the X chromosome do not show accelerated protein evolution, suggesting that new beneficial amino acid mutations are not, on average, recessive (Betancourt, Presgraves, and Swanson 2002). However, the X and autosomes differ when it comes to the lengths of non-coding DNA: the non-neutral evolution of small insertions and deletions has led to longer introns on the X chromosome in D. melanogaster (Presgraves 2006).
We are studying the evolutionary history and genetics of Segregation Distorter (SD), an autosomal meiotic drive gene complex in D. melanogaster. Fifty years of continuous intensive work, culminating in recent breakthroughs on the molecular genetic and cell biological basis of distortion, make SD the best characterized meiotic drive element known. However, important evolutionary questions concerning its origin and population genetic history remain (e.g., Presgraves 2007, 2008). In African populations, for instance, we have found that the SD complex has experienced an enormous recent selective sweep (Presgraves et al. 2009).