Identification of gene classes in canine mammary samples. (a) Hierarchical clustering of dog samples based on a subset of 1043 genes selected by 1-way ANOVA (q-value < 0.001). For display purposes, samples in each class (normal, intermediate-benign, malignant) were clustered separately and arranged from normal (left) to malignant (right). Genes were grouped in six groups according to their pattern of expression (see description in the text) and hierarchically clustered separately. The gene size of each group is indicated to the right of each cluster. (b) Graphical representation of the significance of gene set enrichment for the six gene groups described in (a). Enrichment scores are computed by one-sided Fisher's exact test, using the entire set of orthologous genes represented on both human and dog microarray platforms as the reference population.