The density of protein-coding sequence variation in ExAC reveals a number of properties of human genetic variation undetectable in smaller data sets. For instance, 7.9% of HQ sites in ExAC are multiallelic (multiple different sequence variants observed at the same site), close to the Poisson expectation of 8.3% given the observed density of variation, and far higher than observed in previous data sets - 0.48% in 1000 Genomes (exome intervals) and 0.43% in ESP.
