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Gene–environment interaction (or genotype–environment interaction or G×E) is when two different genotypes respond to environmental variation in different ways. A norm of reaction is a graph that shows the relationship between genes and environmental factors when phenotypic differences are continuous. They can help illustrate GxE interactions. When the norm of reaction is not parallel, as shown in the figure below, there is a gene by environment interaction. This indicates that each genotype responds to environmental variation in a different way. Gene–environment interactions are studied to gain a better understanding of various phenomena. In genetic epidemiology, gene-environment interactions are useful for understanding some diseases. Sometimes, sensitivity to environmental risk factors for a disease are inherited rather than the disease itself being inherited. Individuals with different genotypes are affected differently by exposure to the same environmental factors, and thus gene-environment interactions can result in different disease phenotypes. For example, sunlight exposure has a stronger influence on skin cancer risk in fair-skinned humans than in individuals with darker skin. Nature versus nurture debates assume that variation in a trait is primarily due to either genetic differences or environmental differences. However, the current scientific opinion holds that neither genetic differences nor environmental differences are solely responsible for producing phenotypic variation, and that virtually all traits are influenced by both genetic and environmental differences.〔Ridley, M. (2003) ''Nature via Nurture: Genes, Experience, & What Makes Us Human''. Harper Collins. ISBN 0-00-200663-4〕〔Rutter, Michael. (2006) ''Genes and Behavior: Nature-Nurture Interplay Explained'' Oxford, UK: Blackwell Publishers〕〔Cuhna, Flavio and James J. Heckman ''Investing in Our Young People'', in A. J. Reynolds, A. Rolnick, M. M. Englund, & J. Temple, eds., Cost-effective Early Childhood Programs in the First Decade: A Human Capital Integration, Chapter 18, pp. 381-414, 2010, New York: Cambridge University Press〕 Statistical analysis of the genetic and environmental differences contributing to the phenotype would have to be used to confirm these as gene-environment interactions. == Definitions == There are two different conceptions of gene–environment interaction. Tabery has labeled them ''biometric'' and ''developmental'' interaction, while Sesardic〔Sesardic, N. (2005). ''Making sense of heritability''. Cambridge: Cambridge University Press, p. 48.〕 uses the terms ''statistical'' and ''commonsense'' interaction. The biometric (or statistical) conception has its origins in research programs that seek to measure the relative proportions of genetic and environmental contributions to phenotypic variation within populations. Biometric gene–environment interaction has particular currency in population genetics and behavioral genetics.〔 Any interaction results in the breakdown of the additivity of the main effects of heredity and environment, but whether such interaction is present in particular settings is an empirical question. Biometric interaction is relevant in the context of research on individual differences rather than in the context of the development of a particular organism.〔Tabery, James and Griffiths, Paul E. (2010). Historical and Philosophical Perspectives on Behavioral Genetics and Developmental Science", in Hood, Halpern, Greenberg, and Lerner (Eds.), ''Handbook of Developmental Science, Behavior, and Genetics''. Wiley-Blackwell, pp. 41-60.〕 Developmental gene–environment interaction is a concept more commonly used by developmental geneticists and developmental psychobiologists. Developmental interaction is not seen merely as a statistical phenomenon. Whether statistical interaction is present or not, developmental interaction is in any case manifested in the causal interaction of genes and environments in producing an individual's phenotype.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gene–environment interaction」の詳細全文を読む スポンサード リンク
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