Nat. Immunol. 10, 655–664 (2009); published online 17 May 2009; corrected after print 18 May 2009, 19 August 2009 and 12 March 2010; addendum published online 12 March 2010.

In the version of this article initially published, two values on page 657, the title to Figure 3 and several Supplementary Table citations are incorrect. Sentence 2 of paragraph 2 on page 657, column 2, should end “than those in similar wild-type populations (55% and 61%, respectively).” The title for Figure 3 should begin “RAG-1 cleavage marks paired immunoglobulin alleles differently....” The Supplementary Table citations should be as follows: Figure 3 legend, “(complete statistical results, Supplementary Tables 4–6)”; Figure 5 legend, “(complete statistical results, Supplementary Tables 1, 2, 4, 5, 7 and 8)”; Figure 8 legend, “(complete statistical results, Supplementary Tables 1, 5 and 12)”; and page 662, column 2, sentence 2 “Supplementary Tables 1 and 4.” The errors have been corrected in the HTML and PDF versions of the article.