Variation in gene expression across tissues, and within and between species. (A) Principal component analysis (PCA) plot of the first two principal components of variation in gene expression across five different tissues for five collared flycatchers (red) and five pied flycatchers (blue). (B) Venn diagram of differentially expressed genes across the five tissues. Numbers indicate the number of genes in each category. The number of genes not differentially expressed in any of the tissues is provided in the bottom right corner. (C–G) PCA plots of the first two principal components of variation in gene expression separately for the five different tissues. Ellipses indicate the species-specific mean with a range of ±1 standard deviation, in red for collared flycatchers, in blue for pied flycatchers.
