The larger sample sizes in the exon and low coverage projects allowed us to detect a large number of low frequency variants (MAF < 5%, Fig. 1b). Compared to the distribution expected from population genetic theory (the neutral coalescent with constant population size) we saw an excess of lower frequency variants in the exon project, reflecting purifying selection against weakly deleterious mutations and recent population growth. There are signs of a similar excess in the low coverage project SNPs, truncated below 5% variant allele frequency by reduction in power of our call set to discover variants in this range, as discussed further below.
