Distribution of P/A frequencies among 80 Arabidopsis accessions. (A) Number of P/A genes vs. absent allele frequency. (B) Expected increase of P/A genes relative to the number of sampled accessions, based on a random sampling model. Each datapoint represents an average number of P/A genes for 10000 random simulation samples, and the 95% confidence intervals were also indicated. For example, when 4 accessions are sampled, 919 absent genes are expected.