Hierarchical clustering demonstrated that expression profiles accurately recapitulate tissue type, with blood samples forming the primary outgroup (Fig. 1A). The multiple brain regions cluster strongly together as a single unit, but among those the 11 individual sub-sampled regions are less distinct (Fig. 1A and fig. S4A). The most distinct brain region is the cerebellum (fig. S4A) (16), with preservation method having little impact on that signal (fig. S4B). The distribution of gene expression across tissues is described by Melé et al. (17), who show that tissue-specific transcription is typically dominated by a few genes that vary from tissue to tissue.
