We carried out two distinct types of genetic analysis with data from the National Longitudinal Study of Adolescent Health. The first was a non-DNA twin analysis using monozygotic (identical) and same-sex dizygotic (fraternal) twins. The second analysis investigates the association between age at first sexual intercourse and the 48-bp repeat polymorphism in the dopamine receptor D4 gene (DRD4). The twin analysis shows that MZ twins correlate their timing of first sex to a much greater extent than do the same-sex DZ twins. Our analysis of the polymorphisms in DRD4 indicates that those with an any-3R genotype experienced a risk of first sexual intercourse 23% (p = .016), 233% (p = .0001), 28% (p = .012), and 69% (p = .006) higher than those with an other/other (or any-4R) genotype in the all-ethnicities (n = 2,552), Asian, white, and Hispanic samples, respectively. The risk of first sex does not differ between the two genotypes in the African American sample. These results were obtained after adjusting the standard socioeconomic covariates, including gender, parental education, family structure, and community poverty in the regression model. Evidence from both twin and genetic-variant analyses points to a role of genes in the timing of first sexual intercourse.
In this study, we set out to investigate whether introducing molecular genetic measures into an analysis of sexual partner variety will yield novel sociological insights. The data source is the white male DNA sample in the National Longitudinal Study of Adolescent Health. Our empirical analysis has produced a robust protective effect of the 9R/9R genotype relative to the Any10R genotype in the dopamine transporter gene (DAT1). The gene-environment interaction analysis demonstrates that the protective effect of 9R/9R tends to be lost in schools in which higher proportions of students start having sex early or among those with relatively low levels of cognitive ability. Our genetics-informed sociological analysis suggests that the "one size" of a single social theory may not fit all. Explaining a human trait or behavior may require a theory that accommodates the complex interplay between social contextual and individual influences and genetic predispositions.Risky sexual behavior often plays a critical role in the spread of sexually transmitted diseases (STD), including HIV among adolescents and young adults (IOM 1997). Sociological work on risky sexual behavior has demonstrated the importance of social contexts at the levels of individual, family, neighborhood, and school (Brewster 1994;Browning et al 2005;Furstenberg et al 1987). In this study, we set out to investigate whether introducing molecular genetic measures into analysis of sexual partner variety will lead to novel sociological insights.The notion that individuals may differ with respect to genetic predispositions is not new. Twins and siblings have long been used to estimate the proportion of variance in an outcome due to innate influences, but the findings have frequently been questioned because the two fundamental assumptions of equal environment and assortative mating remain controversial.Earlier efforts linking genetic variants and human outcomes often suffer from small sample sizes, population admixture, multiple testing, inappropriate controls, and non-replication (Cardon and Palmer 2003;Ioannidis et al 2001;Ioannidis et al 2003). Convincing evidence arrived recently. The year 2007 saw an unprecedented succession of discoveries in the genomics of complex traits (e.g., Frayling et al 2007;Pennisi 2007;Scott et al 2007;Sladek et al 2007;Steinthorsdottir et al 2007;Zeggini et al 2007). These discoveries identified genetic variants associated with acute lymphoblastic leukemia, obesity, type 2 diabetes mellitus, prostate cancer, breast cancer, and coronary heart disease. All of the evidence has been replicated multiple times in large independent samples. These discoveries in human genetic NIH Public Access Author ManuscriptAJS. Author manuscript; available in PMC 2010 June 3. If individuals do differ in genetic susceptibilities for diseases, it will be a small stretch to suggest that individuals may also differ in genetic propensities for other traits and behaviors that are of interest to sociologists. The important question, however, is wheth...
The dopamine transporter gene (DAT1) codes for a dopamine transporter protein, which limits the level and duration of dopamine receptor activation. The DAT1 gene is a strong candidate gene for rewardseeking behavior. This article reports compelling evidence for the association between the 40 bp variable number of tandem repeats in the DAT1 gene and the self-reported number of sexual partners among young adults in the United States using the sibling subsample of more than 2500 individuals who participated in the National Longitudinal Study of Adolescent Health. We performed tests of genotypegender interaction as well as analyses stratified by gender. Among the males, possessing one or two alleles of the 10 repeat is associated with an 80-100% increase (Po0.0001, 2df) in the number of sexual partners as compared with the homozygotes for the 9 repeat. The association holds in race/ethnicity-stratified analyses, in Allison's procedure that tests population stratification, and in within-family fixed-effects models. Covariate adjustment for a standard set of socioeconomic factors including religiosity, family structure, parental education, marital and cohabitation history, and neighborhood poverty did not attenuate these associations. Discussion is provided why this finding is absent among females.
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