Nat. Biotechnol. 30, 434–439 (2012); published online 22 April 2012; corrected online 23 April 2012; corrected after print 7 June 2012

In the version of this article initially published online, in the Online Methods “Ion Torrent Sequencing” section, the sentence beginning with “Ten milligrams of this DNA was fragmented with a Bioruptor instrument....” should have read “Ten micrograms....” and in the “454 GS Junior sequencing” section, “(500 total)” should have read “(500 ng total).” The errors have been corrected in the PDF and HTML versions of this article.