Figure 4.

Relationship between samples according to the expression of genes with different reversibility characteristics. PCAs are shown on the left for (a) the slowly reversible and irreversible genes (n = 34) and (b) the most rapidly reversible genes (n = 46). (c) False-color heatmaps are shown on the right for the slowly reversible and irreversible genes (top) and the most reversible tertile of rapidly reversible genes (bottom). Never, former, and current smokers are colored in orange, purple, and green respectively. The PCA and heatmaps were constructed using gene expression data normalized to a mean of zero and a standard deviation of 1. Never and current smokers are organized according to increasing age and former smokers are ordered by decreasing time since quitting smoking (denoted by the gradient) along the sample axis in the heatmap. Affymetrix identifications and HUGO gene symbols are listed for each gene as well as membership in two over-represented functional categories by EASE analysis.

Beane et al. Genome Biology 2007 8:R201   doi:10.1186/gb-2007-8-9-r201
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