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date: 29 March 2020

Abstract and Keywords

Twin studies and behavior genetics address the questions raised by the nature versus nurture debate. Their aim is to estimate the extent to which individual differences in complex traits or phenotypes result from genetic and environmental influences. The vast majority of human behaviors and characteristics are complex traits and are influenced by both genetic and environmental influences, as well as the interplay between these two. Based on the differing genetic relatedness of monozygotic co-twins and dizygotic co-twins, the classical twin model allows for an estimation of the relative importance of these etiological factors. The classical twin model can be extended in multiple ways, depending on the phenotype, research question, and research design. In addition to the classical twin methodology, several such extensions are described in this chapter.

Keywords: Twin modeling, classical twin model, behavior genetics, individual differences, genes, environment, nature-nurture debate, monozygotic twins, dizygotic twins, path diagram, structural equation modeling

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