Consequences of assortative mating for genetic similarities between partners, siblings, and in-laws

Non-random mating by assortment on heritable traits can have consequences for the genetic resemblance between siblings and in-laws in succeeding generations. We studied polygenic scores and phenotypic data from pairs of partners (26,681), siblings (2,170), siblings-in-law (3,905), and siblings-co-in-law (1,763) in the Norwegian Mother, Father and Child Cohort Study. Using structural equation models, we estimated associations between latent genetic and phenotypic variables without measurement error. We found evidence of genetic similarity between partners for educational attainment (rg=0.37), height (rg=0.13), and depression (rg=0.03). Common genetic variants related to educational attainment correlated between siblings above 0.50 (rg=0.68) and between siblings-in-law (rg=0.25) and siblings-co-in-law (rg=0.09). There was indirect assortment on proxy traits for education and depression but not height. Comparisons between the genetic similarities of partners and siblings indicated that genetic variances were in intergenerational equilibrium. This study shows that assortative mating has influenced the genetic structure of extended families for several generations.