MACCOBY of a genetic predisposition are strongly seen under one set of envi- GXE Interactions in Adoption Studies

genetically at-risk infants by a nurturant mother (Anisman et al 1998).We see here that the effects ronmental (rearing) conditions but not another. Of course it is not possible to carry out systematic experiments of this sort with humans, but quantitative genetic studies can be used to test for G E interactions. However, in such studies it is no longer possible to bypass measures of the environ- ment and estimate E effects only as a residual after G effects have been estimated and subtracted out. Instead, there must be direct measures of both G and E. In most it is difficult if not impossible to use the twin design estimate the overall contribution of genotype-environment interaction to phenotypic variance" (plomin 1986:96).3 Since that time, there have been some innovations in utilizing twin studies to study interactions. One method is to use one twin's characteristic as an index to the co-twin's genetic risk; when the two are not highly concordant for the trait, their respective environments can then be examined for clues as to the origins of their .