Correction in Figure 7 Shankar Vembu, University of Toronto 1 August 2014 This comment is to correct an error in Figure 7 (Right) of the paper. One of the SNV population frequencies of node c is incorrectly specified as 0.98; it's correct value is 0.99. This is a typographical error and does not change the results of the paper. We apologize for any inconvenience. -- Authors of the paper Competing interests No competing interests.