Shirley McGuire

Parent ratings of EAS temperaments in twins, full siblings, half siblings, and step siblings

A twin/family design was used to explore genetic contributions to personality; to evaluate whether twins and nontwins yield different genetic results; and to test for the presence of contrast effects, the tendency of a rater to contrast one sibling with the other, thereby magnifying existing behavioral differences. The sample consisted of 708 adolescent same-sex sibling pairs from 10 to 18 years of age. Pairs included identical (monozygotic; MZ) and fraternal (dizygotic; DZ) twins, and full siblings in nondivorced families; and full, half, and unrelated siblings in stepfamilies. Mothers and fathers rated the temperament of their children on the EAS Temperament Survey (A. H. Buss & R. Plomin, 1984). Model-fitting analyses revealed significant genetic influences on each of the four EAS dimensions; however, for some dimensions, heritability estimates were significantly greater for twins than for nontwins. Overall, the data were best described by a sibling interaction model, which indicated significant contrast effects.

Genetic and Environmental Contributions to Loneliness in Children

This report presents the results of the first behavioral genetic studies of childrens loneliness. Data were collected using both an adoption design and a twin-sibling design. As part of the Colorado Adoption Project, 133 sibling pairs (69 biologically related pairs and 64 unrelated pairs in adoptive families) completed a general loneliness scale when they were 9, 10, 11, and 12 years old. As part of the San Diego Sibling Study, 142 sibling pairs (22 monozygotic twin, 40 dizygotic twin, and 80 full-sibling pairs) between the ages of 8 and 14 years old completed a scale assessing loneliness at school. Both studies showed significant heritability and nonshared environmental influences for childrens loneliness.

Genetic and environmental contributions to body mass index: comparative analysis of monozygotic twins, dizygotic twins and same-age unrelated siblings

Background:Earlier studies have established that a substantial percentage of variance in obesity-related phenotypes is explained by genetic components. However, only one study has used both virtual twins (VTs) and biological twins and was able to simultaneously estimate additive genetic, non-additive genetic, shared environmental and unshared environmental components in body mass index (BMI). Our current goal was to re-estimate four components of variance in BMI, applying a more rigorous model to biological and virtual multiples with additional data. Virtual multiples share the same family environment, offering unique opportunities to estimate common environmental influence on phenotypes that cannot be separated from the non-additive genetic component using only biological multiples.Methods:Data included 929 individuals from 164 monozygotic twin pairs, 156 dizygotic twin pairs, five triplet sets, one quadruplet set, 128 VT pairs, two virtual triplet sets and two virtual quadruplet sets. Virtual multiples consist of one biological child (or twins or triplets) plus one same-aged adoptee who are all raised together since infancy. We estimated the additive genetic, non-additive genetic, shared environmental and unshared random components in BMI using a linear mixed model. The analysis was adjusted for age, age2, age3, height, height2, height3, gender and race.Results:Both non-additive genetic and common environmental contributions were significant in our model (P-values<0.0001). No significant additive genetic contribution was found. In all, 63.6% (95% confidence interval (CI) 51.8–75.3%) of the total variance of BMI was explained by a non-additive genetic component, 25.7% (95% CI 13.8–37.5%) by a common environmental component and the remaining 10.7% by an unshared component.Conclusion:Our results suggest that genetic components play an essential role in BMI and that common environmental factors such as diet or exercise also affect BMI. This conclusion is consistent with our earlier study using a smaller sample and shows the utility of virtual multiples for separating non-additive genetic variance from common environmental variance.

Sibling socialization: The effects of stressful life events and experiences

Stressful life events and experiences may disrupt the typical day-to-day interactions between sisters and brothers that provide the foundation of sibling socialization. This chapter examines four experiences that may affect patterns of sibling interaction: parental marital conflict, parental divorce and remarriage, foster care placement, and a siblings developmental disability. We propose a model to guide future research on sibling socialization in distressed families and special populations in which qualities of the sibling relationship moderate the effects of stressful life experiences on child and family adjustment.

The Heritability of Parenting

This tutorial introduces and discusses behavioral genetic research on the heritability of parenting beliefs and behaviors. The article begins with a discussion of the concept of heritability and is followed by a description of behavioral genetic methods and designs. A summary of current research is included, and the limitations of these studies are discussed. The tutorial concludes with a summary and suggestions for future collaborative work.

Parenting as Phenotype: A Behavioral Genetic Approach to Understanding Parenting

SYNOPSIS This article discusses the behavioral genetic (BG) approach to parenting. Parenting is considered a phenotype that can be influenced by nature and nurture. Genetic contributions to parenting are conceptualized as evidence of genotype–environment correlation (rGE). Early BG studies focused on demonstrating that some parenting dimensions were heritable due to passive and evocative rGE processes. Current studies are investigating moderators and mediators of genetic and environmental contributions to parenting. The paper uses parent and child report data on parental warmth from the Twins, Adoptees, Peers, and Siblings study to illustrate the BG approach. Results show that heritability is significant for parent and child reports, but environmental influences differ by information source. Three questions are addressed concerning the BG approach to parenting: What is the nature of parenting? How does the approach inform parenting practice and interventions? What are the future directions?

Children's reactions to the unfamiliar in middle childhood and adolescence: an observational twin/sibling study

Abstract This report presents the results of a twin/sibling observational study of childrens reactions to the unfamiliar. The investigation was designed to examine genetic and environmental contributions to childrens social and exploratory behavior in novel contexts during middle childhood and adolescence. The study included 156 children in 78 same-sex dyads (20 MZ twin pairs, 19 DZ twin pairs, and 39 full sibling pairs) between the ages of eight and 14 years old and their mothers. Each member of the sibling dyad was filmed in three situations (with an unfamiliar adult, alone, and with an unfamiliar peer) in a structured laboratory setting. Mothers’ reports of the childrens extraversion and emotionality were significantly correlated with childrens reactions to the unfamiliar. There were significant genetic and nonshared environmental contributions to childrens behaviors in all three contexts. There were also significant genetic contributions to stability in childrens exploratory behavior from the adult to the peer situation, but not from the alone setting to the adult or to the peer settings. The importance of genetic contributions and context effects for understanding personality differences during middle childhood and adolescence is discussed.

The Sibling Relationship as a Source of Shared Environment

Siblings are many children’s most constant social companions and evidence is building that the sibling relationship serves an important role in children’s development. Behavioral genetic (BG) studies of sibling relationships have shown some evidence of genetic contributions to sibling interaction. The majority of the variance, however, appears to be shared environmental, making the sibling relationship a prime candidate for research on family environment influences. BG studies can further our understanding of sibling socialization effects on children’s development by exploring additional dimensions of the sibling relationship and investigating the joint influences of siblings and peers.

Fullerton Virtual Twin Study: An Update

Virtual twins (VTs) are same-age unrelated siblings reared together from early infancy. These unique sibling sets replicate twinship, but without the genetic link. The first VT pair was identified and studied at the University of Minnesota in 1990, launching the development of the Fullerton Virtual Twin Study at California State University, Fullerton (CSUF) in 1991. The registry currently includes 151 pairs, mostly children, with new pairs identified on a continuous basis. Research with VTs includes studies of general intelligence, body size, interpersonal trust, social coordination, social networks, and parenting. In some cases, VTs have been studied in conjunction with pairs of monozygotic twins, dizygotic twins, full siblings, and friends as part of TAPS (Twins, Adoptees, Peers and Siblings), a collaborative project conducted between CSUF and the University of San Francisco, 2002-2006. VTs will also serve as a comparison group for epigenetic analyses of young Chinese twins reared apart and together.