11th Annual IGSS Conference • September 24, 2020

Integrating Genetics and the Social Sciences 2020

Unpacking social genetic effects in adolescence and young adulthood

Sam Trejo, Public Affairs and Sociology, University of Wisconsin

Recent work has begun to suggest that genome-wide association studies (GWAS) are not only detecting only the direct genetic effect (DGE) of an individual's own genotype on their phenotype, but also the social genetic effects of individuals with whom they interact. A social genetic effect (SGE), also known as an indirect genetic effect, is the influence of one organism's genotype on a different organism's phenotype0. The idea of SGEs originated in evolutionary theory, and SGEs have been observed in animal populations. Social scientists are now beginning to study such SGEs in human populations; examples include among social peers, sibling pairs, and parents and their children. Little is known about the genetic architecture of SGEs, in large part due to the dearth of existing data sets that contain both individual genotype and information about social relationships. Nonetheless, developing a better understanding of the extent and nature of SGEs is important for several reasons. First, given the mechanical positive correlation between genotype within families as well as the observational positive correlation between genotype within social peer groups, understanding the relative magnitude of DGEs and SGEs and the genetic correlation between them is crucial for interpretation GWAS of DGEs (which typically do not control for SGEs). Second, SGEs may provide researchers a useful lens through which to observe how environments influence social, economic, and health outcomes. The genetic pathways discovered in GWASs offer researchers a puzzle to unpack; understanding why some phenotypes have strong versus weak SGEs, or why DGEs and SGEs are more versus less linked, could help researchers glean insight into the underlying social mechanisms at play. We explore social genetic effects among adolescents ages 18 to 22, a critical period for social development. Our analyses will test for SGE using polygenic scores derived from existing large scale GWAS for a wide range of phenotypes; we overcome non-random peer group formation by focusing on only randomly assigned roommates and dorm mates. The longitudinal nature of our data also allows us to test if SGEs fade out as social relationships change over time (for example, we could look at the association of freshman year roommate's genetics on drinking behavior in each year of college to test if the association becomes smaller in later years).

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