Genes and the environment mutually influence one another. One way to investigate these bidirectional interactions between genes and environment is to examine monozygotic twins. One of the studies dedicated to the issue of the gene-environment interaction of fragile x syndrome in twins was performed by Willemsen et al. (2000). The authors analyzed monozygotic twin sisters’ case, one of whom is affected by a full mutation in the FMR1 gene and is mentally handicapped. The production of an FMRP protein, which is presented in the brain and develops connections between synapses, depends on this FMR1 gene. Another sister is not affected by the mutation and has normal mental development. Willemsen et al. (2000) analyzed the blood cells of the twins. This analysis showed that the normal sister’s X chromosome is active in all blood cells, whereas her sister’s X chromosome “inactive in approximately 50% of her blood cells” (Willemsen et al., 2000, p. 603). The work concludes that inactivation of the X chromosome when the embryos of the twins became separated.
It is essential to study gene-environment interactions because it could improve population health. The investigation of these interactions is possible through the examination of monozygotic twins reared apart. This method was used by Bergeman et al. (1988) to test how different environments affect identical genotypes. Bergeman et al. (1988) analyze 99 pairs of such twins to see the differences in personalities between tweens who were parented separately.
Another method to explore interactions between genes and environment is multivariate modeling. This method could be illustrated by the research conducted by Gillespie et al. (2004). The scholars analyzed the Junior Eysenck Personality Questionnaire scores taken by more than 540 twin pairs via genetic simplex modeling. Gillespie et al. (2004) discovered that genetic variations in twins at the age of 14 – 16 years could be explained by genetic variations present in them at the age of 12.
References
Bergeman, C. S., Plomin, R., McClearn, G. E., Pedersen, N. L., & Friberg, L. T. (1988). Genotype Environment interaction in personality development: Indentical twins reared apart. Psychology and aging, 3(4), 399–406.
Gillespie, N. A., Evans, D. E., Wright, M. M., & Martin, N. G. (2004). Genetic simplex modeling of Eysenck’s dimensions of personality in a sample of young Australian twins. Twin Research and Human Genetics, 7(6), 637-648.
Willemsen, R., Olmer, R., Otero, Y. D. D., & Oostra, B. A. (2000). Twin sisters, monozygotic with the fragile X mutation, but with a different phenotype. Journal of medical genetics, 37(8), 603-604.