Characteristics of HARs (human accelerated regions)

...they are:
- A/T to G/C changes (weak to strong)
- located in high recombination areas
- next to genes that are enriched for transcription factors
- located in high G/C content areas near telomeres

Forces Shaping the Fastest Evolving Regions in the Human Genome

Katherine S. Pollard, Sofie R. Salama, Bryan King, Andrew D. Kern, Tim Dreszer, Sol Katzman1, Adam Siepel, Jakob S. Pedersen, Gill Bejerano, Robert Baertsch, Kate R. Rosenbloom, Jim Kent, David Haussler

PLoS Genetics vol. 2 issue 10; October 2006

Abstract: Comparative genomics allow us to search the human genome for segments that were extensively changed in the last ~5 million years since divergence from our common ancestor with chimpanzee, but are highly conserved in other species and thus are likely to be functional. We found 202 genomic elements that are highly conserved in vertebrates but show evidence of significantly accelerated substitution rates in human. These are mostly in non-coding DNA, often near genes associated with transcription and DNA binding. Resequencing confirmed that the five most accelerated elements are dramatically changed in human but not in other primates, with seven times more substitutions in human than in chimp. The accelerated elements, and in particular the top five, show a strong bias for adenine and thymine to guanine and cytosine nucleotide changes and are disproportionately located in high recombination and high guanine and cytosine content environments near telomeres, suggesting either biased gene conversion or isochore selection. In addition, there is some evidence of directional selection in the regions containing the two most accelerated regions. A combination of evolutionary forces has contributed to accelerated evolution of the fastest evolving elements in the human genome.