Candidate genes for criminal and delinquent behavior

INTRODUCTIONBehavioral genetic research seeks to estimate the relative contribution of genetic and non-genetic factors on variance in human traits and behaviors. The findings of this line of research have consistently revealed that genetic factors are associated with the development of virtually every human characteristic (Wright, Tibbetts, and Daigle, 2008). During the past 10 years, there has been a growing pool of criminologists who have begun to examine the extent to which genes impact antisocial behaviors, criminal involvement, and criminogenic personality traits (Beaver, 2009). The results of this line of research have consistently revealed that genes, to some degree, are implicated in the etiology of antisocial phenotypes (Walsh, 2011). Although the exact estimates vary across individual studies, the results of four meta-analyses have converged to reveal that, on average, 50% of the variance in antisocial behaviors is accounted for by genetic influences (Ferguson, 2010; Mason and Frick, 1994; Miles and Carey, 1997; Rhee and Waldman, 2002).Heritability estimates of antisocial behaviors are generated primarily through analysis of kinship pairs, especially twin pairs. In the case of twin studies, samples are analyzed that include monozygotic (MZ) twins, who share 100% of their DNA, and dizygotic (DZ) twins, who share about 50% of their DNA. If the environments of MZ and DZ twins are the same, then the only reason MZ twins should be more similar than DZ twins on a particular phenotype is due to the greater amount of shared genetic material (Plomin et al., 2008). In order to estimate heritability-or the proportion of variance accounted for by genetic factors-twins and co-twins are compared on a measured phenotype and the strength of the relationship between the twins' scores is ascertained by calculating an intraclass correlation. The heritability of a phenotype would be higher in instances where the intraclass correlation for MZ twins is significantly greater than the intraclass correlation for DZ twins. In addition to examining twins, behavioral geneticists also can extend their analyses to other types of kinship pairs, including full siblings, half-siblings, and other relatives.Although the findings of kinship-based research provide insight into the genetic underpinnings to antisocial behaviors, these studies are limited in that they only decompose phenotypic variance. At the same time, they are unable to specify the effects of specific genetic polymorphisms on antisocial behaviors (Ferguson and Beaver, 2009). During the past decade or so, however, researchers have begun to address this limitation by analyzing samples of respondents who have been genotyped. Although this research is still in its infancy, the results of these studies have implicated a number of specific genetic polymorphisms that are associated with criminal behaviors (Beaver et al., 2007; Ferguson and Beaver, 2009; Foley et al., 2004). Despite these findings, studies examining the effects of measured polymorphisms have likely only scratched the surface of the genes linked to criminal behaviors. Consequently, the goal of the current chapter is to 1) introduce genetic concepts and discuss their relevance for criminology, 2) identify a number of genetic polymorphisms that may be associated with delinquent and criminal behaviors, and 3) offer suggestions for future research.A PRIMER ON GENETICSDeoxyribonucleic acid (DNA) is a chemical blueprint found in all cells except red blood cells that permits all living organisms to develop, function, and subsist. Because all humans have a unique chemical code (except MZ twins), DNA can contribute to between-individual differences in nearly every phenotype, including antisocial behaviors (Carey, 2003; Walsh and Beaver, 2009). The structure of DNA consists of two fibers, known as polynucleotides, which wrap around each other to form a double helix (Hartl and Jones, 2009). Aligned along the backbone of each polynucleotide are nucleotides, or bases. …