From both sets of profiles, we can generate a matrix C of expression signatures, comprising marker genes and their expression levels across various cells (fig. S8). In this matrix, a number of genes (e.g., the gene for dopamine receptor DRD3) had expression levels that varied more across cell types than they did in bulk tissue measurements across individuals in a population (Fig. 2A). This suggests that cell-type changes across individuals could contribute substantially to variation in individual bulk expression levels.
