Expected extent of IBD and number of cousins for 1st–10th degrees of cousinship.

aTheoretical expectation of the amount of IBD across the genome shared between nth cousins, assuming 3600 cM across the entire genome. It should be emphasized this description assumes a single common ancestor for a pair of cousins; multiple shared common ancestors will increase the predicted IBD sharing.bThe fraction of nth degree cousins detected using our IBD algorithm and based on simulated pedigrees of up to 10th degree cousins (see Methods).cAssuming a specific model of pedigree and population growth over the past 11 generations (see Methods).dThe expected number of cousins detectable with our IBD algorithm (Ndc) was calculated by multiplying the probability of detecting an nth cousin by the number of nth cousins obtained from our pedigree model of population growth (see Methods).eGiven the variation in population growth at >9 generations ago, combined with a low power of detection for 9th or 10th cousins, we have indicated the number of detectable cousins for those categories as not applicable, “NA”.