Genetic similarity between relatives provides evidence on the presence and history of assortative mating

Abstract

Assortative mating – the non-random mating of individuals with similar traits – is known to increase trait-specific genetic variance and genetic similarity between relatives. However, empirical evidence is limited for many traits, and the implications hinge on whether assortative mating has started recently or many generations ago. Here we show theoretically and empirically that genetic similarity between relatives can provide evidence on the presence and history of assortative mating. First, we employed path analysis to understand how assortative mating affects genetic similarity between family members across generations, finding that similarity between distant relatives is more affected than close relatives. Next, we correlated polygenic indices of 47,135 co-parents from the Norwegian Mother, Father, and Child Cohort Study (MoBa) and found genetic evidence of assortative mating in eight out of fifteen examined traits. The same traits show elevated similarity between relatives, especially distant relatives. Five of the eight traits, including educational attainment, showed greater genetic variance among offspring, which is inconsistent with stable assortative mating over many generations. These results suggest an ongoing increase in familial similarity for these traits. The implications of this research extend to genetic methodology and the understanding of social and economic disparities.

Disentangling direct and indirect genetic effects from partners and offspring on maternal depression using trio-GCTA

“…When assortative mating occurs for a trait, it is generally expected to increase the heritability of the trait. However, two recent studies, both using polygenic scores, did not find evidence of widespread assortative mating for depression in MoBa 63,64 . We note that these studies may have yielded estimates which are biased downwards because of low predictive power of the depression polygenic score itself.…”

Dissecting the contribution of common variants to risk of rare neurodevelopmental conditions

“…Another factor that may contribute to the significant correlation between non-transmitted alleles in parents and neurodevelopmental conditions in their children is parental assortment, the phenomenon whereby people are more likely to choose partners with similar traits to themselves. Parental assortment is known to be particularly strong for educational attainment and cognitive ability, with estimates of phenotypic correlation between spouses ranging from 0.25 to 0.6 [57][58][59][60][61][62][63][64] . It is also observed for psychiatric conditions 63,[65][66][67] , including in parents of autistic individuals and of individuals with neurodevelopmental conditions due to the 16p12.1 deletion 68 .…”

Non-random Mating Patterns in Education, Mental, and Somatic Health: A Population Study on Within- and Cross-Trait Associations

“…Assortment based on heritable mental health should lead to genetic correlations between partners, and since the genes are determined before the couples are formed, correlations should be independent of convergence. Such studies report null-findings for mental disorders 8,9 , except for schizophrenia 10 . Such findings could imply that mental health does not influence partner selection.…”

“…Such studies report null-findings for mental disorders 8,9 , except for schizophrenia 10 . Such findings could imply that mental health does not influence partner selection.…”