Nizamova, E. S. Genetic and Environmental Dependence of Mental Development of Twins

Abstract: The study is devoted to the genetic and environmental dependence of mental development of twins in terms of formation of their ‘Big Five’ basic personal traits (neurotism, extraversion, openness to experience, friendliness and consciousness). The purpose of the study is to define and compare environmental and genetic models which are most typical for each trait. The empiric part of the study covers 319 one-egg and two-egg twins living in Bushevsk, Izhevsk and Tver. A classical twin method was used in the study. Apart of one or two-egg nature, the study also recorded sex, age, nationality and a number of other demographic and anammestic parameters of twins and their parents. Using the method of structural modeling for each of personal trait, for the first time in Russian researches of twins the author of the study described a proper environmental and genetic model assessing contribution of genes and environment into phenotype differences. Received results show the differential nature of genetic-environmental determination of the Big Five charts. The Neorotism, Friendliness and Consciousness Charts are most typically described by the means of models which include additive genetic factors and individual environment. In addition to that, contribution of genetic factors are somewhere between 50 and 59 percent. Extraversion and Openness to Experience charts deal with the environmental model where general and individual environment share equal influence. Using the method of intra pair correlation the author defines non-linear dependences between genotypes, genders and ages. The author also specifies and clarifies peculiarities of demonstration of the Big Five personal traits in groups of one-egg and two-egg twins differing in gender and age.

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