The clustering of tumors taken to the analysis and variation in expression of 20 the mostly significant genes between the most and less malignant canine mammary tumors. A. Differences in expression of genes in 12 examined samples. Data is presented in a matrix format: each row represents a single gene, and each column an experimental sample. In each sample, the ratio of the abundance of transcripts of each gene to the median abundance of the gene's transcript across all tissue samples is represented by the color of the corresponding cell in the matrix. Green squares, transcript levels below the median; red squares, transcript levels greater than the median. Color saturation reflects the magnitude of the ratio relative to the median for each set of samples. B. Boxplots comparing relative signal measured for 20 most significantly changed genes between less malignant (yellow) and the most malignant (green) tumors.