Long runs of homozygosity are correlated with marriage preferences across global population samples

Children of consanguineous unions carry long runs of homozygosity (ROH) in their genomes, due to their parents’ recent shared ancestry. This increases the burden of recessive disease in populations with high levels of consanguinity and has been heavily studied in some groups. However, there has been little investigation of the broader effect of consanguinity on patterns of genetic variation on a global scale. Here, we collect published genetic data and information about marriage practices from 396 worldwide populations and show that preference for cousin marriage has a detectable effect on the distribution of long ROH in these samples, increasing the expected number of ROH longer than 10Mb by a factor of 1.5 (P=2.3 × 10−4). Variation in marriage practice and consequent rates of consanguinity is therefore an important aspect of demographic history for the purposes of modeling human genetic variation. However, marriage practices explain a relatively small proportion of the variation in ROH distribution and consequently the ability to predict marriage practices from population genetic samples (for example of ancient populations) is limited. ### Competing Interest Statement The authors have declared no competing interest.