Hierarchical clustering of the two data sets using all expression profiles. Hierarchical clustering of the cell lines with Ward method and correlation distance using the expression profiles from the Ross (left) and Staunton (right) data sets. The tissues of origin of the cell lines are coded as BR = Breast, CNS = Central Nervous System, CO = Colon, LE = Leukaemia, ME = Melanoma, LU = Lung, OV = Ovarian, PR = Prostate, RE = Renal. The Ward method maximizes the between-cluster inertia and minimizes the within-cluster inertia for each step of the clustering algorithm. Height represents the loss of between-cluster inertia for each clustering step. Dashed lines cut the dendrograms to highlight the three main clusters.