Sections of the genome that are largely conserved across mammals and even the entire animal kingdom, but differ in humans, are known as human accelerated regions (HARs). Deciphering their function may prove key to understanding what sets humans apart from other organisms. For example, 2xHAR.142 and 2xHAR.114, like many other HARs, function as enhancers, which increase or decrease the level of a gene’s expression.

Click the HAR in the chromosome segment to see a comparison of the human and chimp sequences. Click embryo illustrations to view photographs of the lacZ staining in real mouse embryos.


Location: Typically outside genes, though some HARs are found in gene introns
Size: Just 227 base pairs long, on average
Function: Most HARs studied so far are enhancers, sequences of DNA that increase or decrease the expression of a gene.

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