PCA plot of the integrated mouse gene expression data matrix. Each dot represents a sample, which is colored by the annotation of its tissue type. The samples can be loosely divided in four areas from left to right: nervous system (blue), muscle/heart (red), cell line (green) and others, and liver (purple). The brown dots co-clustering with nervous system samples are retina samples. Samples with unknown organism part (-) are white so they are invisible.
Zheng-Bradley et al. Genome Biology 2010 11:R124 doi:10.1186/gb-2010-11-12-r124