Comparison of biological versus technical variation for matched replicate samples. The data are represented as volcano plots of three MZ twin pairs (1035, 3014 and 2034; black) with an overlay of matched technical replicate DNA sample (gray). The x-axis represents the M-value fold change of variation across the four samples in each pair (replicate samples for each of twin 1 and 2 at birth and 18 months). The y-axis represents the -log10 FDR adjusted P-value for the moderated paired t-test. A genome-wide significance (FDR <0.1 for each individual pair) is denoted by the dotted horizontal line. In general, variation between biological replicates exceeds genome-wide significance and technical variation falls below genome-wide significance.