Figure 1

Method for quantifying similarity between gene expression profiles and assessing significance. (a) The aging to young ratio of gene expression is calculated and log-transformed for all genes or orthologous genes present on both of the compared microarrays. Ortholog pairs need to be identified in cross-species comparisons. (b) Two example scatter plots for comparisons of change in gene expression with age. The calculated correlations (Pearson; R) are displayed to the lower right in the plots. (c-e) A distribution of correlations is produced by randomly pairing the genes present on both microarrays 10,000 times and calculating the Pearson correlation for each permutation. The distribution of random correlations (Monte Carlo simulation) is displayed as a density curve in (e). The actual correlation, indicated by an arrow in (e), can then be compared to the random distribution of correlations.