Investigators at Duke University report in a PNAS paper published online in advance this week on their use of human artificial chromosome assembly assays, with which they show that "both D17Z1 and D17Z1-B can support de novo centromere assembly independently." This study, the authors say, illustrates the "presence of centromeric epialleles on an endogenous human chromosome" and points to the "genomic complexities underlying the mechanisms that determine centromere identity in h