Influence of MT on correlation between probesets. The distribution of Pearson correlation for all probeset pairs (black) vs. MT probeset pairs (red). Data from 50 arrays from Gene Atlas processed with RMA. The global (black) curve represents correlation for 1 million random probeset pairs, while the MT curve (red) was drawn using all probeset pairs from over 110,000 PTP motifs that occur in the HG_U133A array. The peak of the MT curve close to a correlation of 1 may be explained by a group of probesets having almost constantly high signal. Most of these are 'hub' probesets as defined in the text. The green distribution is a normal distribution with the same mean ( = 0.018) and standard deviation as the black one. It can be seen that the global distribution is very close to normal.