Human and chimpanzee promoter activity and mRNA expression in tissues. (a) Promoter activity in cell cultures. Normalized activities of promoters of the indicated genes are compared to the average of the three human and the three chimpanzee clones for each cell line and promoter indicated. Blue indicates lower activity than average, whereas yellow indicates higher activity. The color scale for the fold-change is below. Significant differences in activity between the two species are indicated by red frames. (b) Expression of the genes in tissues as assayed by mRNA levels measured by oligonucleotide arrays for brain and liver . The values are averages of the three human and three chimpanzee individuals for which expression levels were determined  and are compared to the average level of the corresponding gene.