Educational attainment influences levels of homozygosity through migration and assortative mating

Abstract

Individuals with a higher education are more likely to migrate, increasing the chance of meeting a spouse with a different ancestral background. In this context, the presence of strong educational assortment can result in greater ancestry differences within more educated spouse pairs, while less educated individuals are more likely to mate with someone with whom they share more ancestry. We examined the association between educational attainment and F roh (= the proportion of the genome consisting of runs of homozygosity [ROHs]) in ~2,000 subjects of Dutch ancestry. The subjects' own educational attainment showed a nominally significant negative association with F roh (p = .045), while the contribution of parental education to offspring F roh was highly significant (father: p < 10(-5); mother: p = 9 × 10(-5)), with more educated parents having offspring with fewer ROHs. This association was significantly and fully mediated by the physical distance between parental birthplaces (paternal education: pmediation = 2.4 × 10(-4); maternal education: pmediation = 2.3 × 10(-4)), which itself was also significantly associated with F roh (p = 9 × 10(-5)). Ancestry-informative principal components from the offspring showed a significantly decreasing association with geography as parental education increased, consistent with the significantly higher migration rates among more educated parents. Parental education also showed a high spouse correlation (Spearman's ρ = .66, p = 3 × 10(-262)). We show that less educated parents are less likely to mate with the more mobile parents with a higher education, creating systematic differences in homozygosity due to ancestry differences not directly captured by ancestry-informative principal components (PCs). Understanding how behaviors influence the genomic structure of a population is highly valuable for studies on the genetic etiology of behavioral, cognitive, and social traits.

Fig 1. Representation of the mediation model described in the section “Migration distance and F _roh”.

The five covariates included in the model (the three PCs reflecting ancestry, city size, and religion) are not shown in this Figure.

Fig 2. Migrations from the parental birthplace to the offspring birthplace.

The average distance the colors are based on are: father: 28.47 km (SD = 44.45); mother: 30.16 km (SD = 44.45). The difference between the moving distance of fathers with a Secondary Education and fathers with a Tertiary Education is best suited to visualize the effect because of the almost equal sample sizes with respect to individuals plotted (i.e., moved) and the significant increase of moving distance (see Table 1); also note that fathers with Secondary Education have >25% measurements in total, which is another indicator of the difference in migration levels.

Fig 3. Association between geography and ancestry per parental educational attainment level.

A—Left: geographic distribution of PC1 (N = ~5,000 unrelated Dutch subjects), where the mean PC1 value per postal code (current living address) was computed, divided into 10 percentiles, and plotted. Right: two plots showing the explained variance (R²) of the offspring’s PC1 by the North-South gradient based on the offspring’s birthplace, per parental educational group. B—Left: geographic distribution of PC2. Right: two plots showing R² between offspring PC2 and the East-West gradient based on offspring’s birth place.