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Family theories have been founded on research that cannot discriminate genetic and environmental influences and, consequently, most theories do not have highly developed models of gene–environment interplay in families. Behavioral genetic approaches, which can identify gene–environment interplay, have typically not been driven by family theories and have lacked adequate measurement of family processes. In this article, the authors describe behavioral genetic mechanisms and methods using representative examples of research on family processes, highlighting the advantages of an integrated approach. New directions in research and theory driven by an integrated approach are discussed.

AbstractThe Nonshared Environment in Adolescent Development (NEAD) project is a longitudinal study of twins/siblings and parents that has been assessed 3 times: middle adolescence, late adolescence and young adulthood (N = 720 families at Time 1). Siblings varied in degree of genetic relatedness including identical twins, fraternal twins, full siblings, half siblings and genetically unrelated (or step) siblings. There were also two family types: nondivorced and step. A multimeasure, multirater approach was taken in NEAD, with data collected from all participants (2 twins or siblings, mother and father) as well as from coded videotaped observations of family interactions. Detailed assessments of family relationships, adolescent adjustment and competence were collected at all 3 times. The original aim of NEAD was to identify systematic sources of nonshared environmental influences that contribute to differences among family members. Although systematic sources of nonshared environmental influences were not found in NEAD, three major sets of findings emerged: (1) genetic influences on family relationships and on associations between family relationships and adolescent adjustment; (2) genetic and environmental influences on adolescent adjustment, comorbidity and stability and change in adolescent adjustment from middle to late adolescence; and (3) genetic influences on relationships outside the family.

This study examined genetic and environmental effects on individual variation in pubertal timing using two national samples of siblings from the Nonshared Environment of Adolescent Development (NEAD) and the National Longitudinal Study of Adolescent Health (Add Health). In each sample, female and male siblings with different degrees of genetic relatedness, i.e., monozygotic twins, dizygotic twins, full siblings, half siblings, and unrelated siblings in blended families, were assessed. Timing of pubertal development was measured by age‐adjusted self‐report measures of the Pubertal Development Scale in NEAD and a four‐item scale of pubertal development in the Add Health. The results indicated that both genetic and environmental influences play an important role in determining the relative timing of pubertal development for both boys and girls.

AbstractFriend support is often assumed to exert direct environmental influences on psychological distress, yet the role of both genetic and environmental influences on this association has not been examined. This study investigates whether both genetic and environmental factors explain the link between friend support and psychological distress in adults. The sample was drawn from the Midlife Development in the United States study and included 947 pairs of monozygotic, same‐sex dizygotic (DZ), and opposite‐sex DZ twins. Results showed that genetic influences explain the association between friend support and psychological distress, suggesting that heritable contributions to friend support also shape psychological distress. Interventions focused on psychological distress should consider how individuals' heritable characteristics influence their friend support and psychological distress.

Deficits in social problem‐solving skills are often associated with antisocial behavior, particularly in children's extrafamilial relationships. The current study was designed to examine this association in several new ways: the association was examined at two times in an adolescent sample within the context of the family; genetic models were used to estimate genetic and environmental effects on observational measures of problem solving and antisocial behavior and on the association between the two. The analyses were conducted as part of the Nonshared Environment in Adolescent Development project, consisting of 720 families at Time 1 (mean adolescent age: 14.5 years) and 440 families at Time 2 (mean adolescent age: 16.1 years). Genetic influence was found for antisocial behavior, but not for problem solving. The findings of shared environmental influences on these measures and their association are unusual in the behavioral genetic literature and are important in that respect.

Prior research has suggested that disadvantaged neighborhood contexts alter the etiology of youth antisocial behavior (ASB). Unfortunately, these studies have relied exclusively on governmental data collected in administratively-defined neighborhoods (e.g., Census tracts or block groups, zip codes), a less than optimal approach for studying neighborhood effects. It would thus be important to extend prior findings of GxE using neighborhood sampling techniques, in which disadvantage is assessed via resident informant-reports of the neighborhood. The current study sought to do just this, examining two independent twin samples from the Michigan State University Twin Registry. Neighborhood disadvantage was assessed via maternal and neighbor informant-reports, the latter of which were analyzed multiple ways (i.e., all neighbors within 1km, nearest neighbor, and all neighbors within the County). Analyses revealed clear and consistent evidence of moderation by neighborhood disadvantage, regardless of informant or the specific operationalization of neighborhood. Shared environmental influences on ASB were observed to be several-fold larger in disadvantaged contexts, while genetic influences were proportionally more influential in advantaged neighborhoods. Such findings indicate that neighborhood disadvantage exerts rather profound effects on the origins of youth ASB. Efforts should now be made to identify the active ingredients of neighborhood disadvantage.

AbstractThe Pennsylvania Longitudinal Study of Parents and Children Twin Registry was developed to capture a representative sample of multiple births and their parents in the state of Pennsylvania. The registry has two main efforts. The first began in 2012 through recruitment of adolescents in Pennsylvania schools. The second effort began in January 2019 in partnership with the Pennsylvania Department of Health to capture the birth cohort of twins born from 2007 to 2017. Study recruitment, sample demographics, focus and measures are provided, as well as future directions.

The Early Growth and Development Study is a prospective adoption study of birth parents, adoptive parents, and adopted children recruited in two cohorts (N= 561 triads). The primary study aims are to examine how family, peer, and contextual processes affect children's adjustment, and to examine their interplay (mediation, moderation) with genetic influences. Participants were recruited through adoption agencies located throughout the United States following the birth of a child. Assessments are ongoing, in 9-month intervals until the child reaches 3 years of age and in 1-year intervals thereafter through age 9. Data collection includes the following primary constructs: child temperament, social behavior, school performance, mental health, and health; birth and adoptive parent personality characteristics, mental health, competence, stress, health, context, substance use, parenting, and marital relations; and pregnancy use of drugs and maternal stress during pregnancy. DNA and salivary cortisol samples have also been collected. Analyses have indicated evidence for genotype-environment interactions during early childhood. Study procedures, sample representativeness (including tests of potential confounds in the adoption design), and an overview of findings to date are summarized, and future plans are described.

AbstractPrevious studies indicate that the emotional quality of marital relationships is mirrored in parent–child relationships. We explored the degree to which these associations are explained by genetic and environmental factors. Participants were drawn from the Twin and Offspring Study in Sweden (TOSS), and included 544 female twin pairs (258 monozygotic [MZ], 286 dizygotic [DZ]), and 311 male twin pairs (128 MZ, 183 DZ). The spouses and one adolescent child of each twin also participated in this study. The twins completed self-report measures that assessed their marital quality and their warmth and negativity towards their children. Observational ratings of marital warmth and negativity, and of maternal warmth and negativity were obtained for a subset of female twin pairs (150 MZ, 176 DZ). Selfreported marital satisfaction was associated with self-reported parental warmth and negativity for mothers (rs = .25, -.36) and fathers (rs = .25, -.44). For the observational measures, marital warmth was associated with maternal warmth (r = .42), while marital negativity was associated with maternal negativity (r = .34). On average genetic factors explained nearly half of the covariance between selfreported marital satisfaction and parenting for mothers (48%) and fathers (47%). Genetic factors explained 21% of the covariance between observed marital and maternal warmth, but did not contribute to associations between marital and maternal negativity. These findings indicate that parents' genetically influenced characteristics help shape the emotional climate of the family.

AbstractThe Early Growth and Development Study (EGDS) is a prospective adoption study of birth parents, adoptive parents and adopted children (n= 561 adoptees). The original sample has been expanded to include siblings of the EGDS adoptees who were reared by the birth mother and assessed beginning at age 7 years (n= 217 biological children), and additional siblings in both the birth and adoptive family homes, recruited when the adoptees were 8–15 years old (n= 823). The overall study aims are to examine how family, peer and contextual processes affect child and adolescent adjustment, and to examine their interplay (mediation, moderation) with genetic influences. Adoptive and birth parents were originally recruited through adoption agencies located throughout the USA following the birth of a child. Assessments are ongoing and occurred in 9 month's intervals until the adoptees turned 3 years of age, and in 1 to 2 year intervals thereafter through age 15. Data collection includes the following primary constructs: child temperament, behavior problems, mental health, peer relations, executive functioning, school performance and health; birth and adoptive parent personality characteristics, mental health, health, context, substance use, parenting and marital relations; and the prenatal environment. Findings highlight the power of the adoption design to detect environmental influences on child development and provide evidence of complex interactions and correlations between genetic, prenatal environmental and postnatal environmental influences on a range of child outcomes. The study sample, procedures and an overview of findings are summarized and ongoing assessment activities are described.

AbstractThe present study uses a parent–offspring adoption design to examine the dual roles of heritable and environmental influences on children's mathematics achievement. Linked sets (N = 195) of adopted children, adoptive parents, and birth parents each completed a measure of mathematics fluency (i.e., simple computational operations). Birth parent mathematics achievement and adoptive father mathematics achievement positively correlated with child achievement scores at age 7, whereas adoptive mother and adopted child mathematics achievement scores were not significantly associated with one another. Additionally, findings demonstrated no significant effects of gene–environment interactions on child mathematics achievement at age 7. These results indicate that both heritable and rearing environmental factors contribute to children's mathematics achievement and identify unique influences of the paternal rearing environment on mathematics achievement in middle childhood.

AbstractThe effect of parental depression on children's adjustment has been well documented, with exposure during early childhood particularly detrimental. Most studies that examine links between parental depression and child behavior are confounded methodologically because they focus on parents raising children who are genetically related to them. Another limitation of most prior research is a tendency to focus only on the effects of maternal depression while ignoring the influence of fathers' depression. The purpose of this study was to examine whether infants' exposure to both parents' depressive symptoms, and inherited risk from birth mother internalizing symptoms, was related to school age children's externalizing and internalizing problems. Study data come from a longitudinal adoption study of 561 adoptive parents, biological mothers, and adopted children. Adoptive fathers' depressive symptoms during infancy contributed independent variance to the prediction of children's internalizing symptoms and also moderated associations between adoptive mothers' depressive symptoms and child externalizing symptoms.