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Human accelerated regions (HARs), first described in August 2006,[1][2] are a set of 49 segments of thehuman genome that are conserved throughoutvertebrate evolution but are strikingly different inhumans. They are named according to their degree of difference between humans andchimpanzees (HAR1 showing the largest degree of human-chimpanzee differences). Found by scanning through genomic databases of multiple species, some of these highlymutated areas may contribute to human-specific traits. Others may represent loss of functional mutations, possibly due to the action of biasedgene conversion[2][3] rather thanadaptive evolution.[4][5][6]
Several of the HARs encompass genes known to produce proteins important in neurodevelopment. HAR1 is a 106-base pair stretch found on the long arm ofchromosome 20 overlapping with part of theRNA genesHAR1F and HAR1R. HAR1F is active in the developing human brain. The HAR1 sequence is found (and conserved) in chickens and chimpanzees but is not present in fish or frogs that have been studied. There are 18 base pair mutations different between humans and chimpanzees, far more than expected by its history of conservation.[1]
HAR2 includesHACNS1 agene enhancer "that may have contributed to the evolution of the uniquely opposable humanthumb, and possibly also modifications in theankle orfoot that allow humans towalk on two legs". Evidence to date shows that of the 110,000 gene enhancer sequences identified in the humangenome, HACNS1 has undergone the most change during theevolution of humans following the split with the ancestors ofchimpanzees.[7] The substitutions in HAR2 may have resulted in loss of binding sites for a repressor, possibly due to biased gene conversion.[8][9]
The HAR regions may be downloaded from:
NCBI:https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE180714