Figure 1

Principle Component Analysis (PCA) of human, mouse and rat tissue expression profiles based on two generations of Affymetrix expression arrays shown as SET 1 (upper plot: Affymetrix HG-U133A, MG-U74Av2, and RG-U34 arrays) and SET 2 (lower plot: Affymetrix Human133 Plus 2.0, Mouse430 2.0, and Rat230 2.0 arrays). A common set of 56 and 55 tissue types, respectively, is represented for each organism. Each tissue type is a single mean expression vector processed from all samples annotated as such in the Genevestigator database. Species are represented by symbols and tissue types are numbered. Tissue types were grouped according to organ systems that are represented by different colors. Related tissues clustered together into an overall consistent architecture between the three species. The two generations of microarrays yielded very similar results, despite being composed of independent and differerent sets of published experiments.