Gene expression differences between humans and chimpanzees. (A) Hierarchical clustering of expression differences between humans and chimpanzees in the prefrontal cortex in the current data set with (PFC) and without (PFC N) masking of the sequence differences between the species and previously published prefrontal cortex (PFC′) and liver data (Enard et al. 2002). All genes differentially expressed in at least one tissue and detected in the other one are shown. The vertical black bar indicates the cluster of expression differences that disappears after the masking procedure. (B) Hierarchical clustering of genes classified as differentially expressed between humans and chimpanzees in at least one out of six studied brain regions. Each row represents a gene and each column represents a pairwise comparison between one human and one chimpanzee in a given tissue. The magnitude of expression differences is shown as the base two logarithm of the ratio of the gene expression level in humans to the one in chimpanzees. Higher expression in humans is shown in red and higher expression in chimpanzees in blue, with color intensity being proportional to the magnitude of the expression difference as indicated by the color bar at the bottom of the figure. (B) Broca's area; (PFC) prefrontal cortex; (PVC) primary visual cortex; (ACC) anterior cingulate cortex; (CN) caudate nucleus; and (CB) cerebellum.
