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 As scientists continue to study the human genome, a growing body of evidence is showing that DNA alone does not necessarily determine one’s destiny. Rather, it appears that "epigenetics", the environmental factors for gene expression, may be a powerful factor in determining whether a disease strikes or not. The term epigenome refers to a series of biochemical processes that enable the genes to be turned on or off (expressed) in certain ways. Although genetic information is uniform among the different cells of a complex organism, the epigenome varies from tissue to tissue, controlling or influencing the differential expression of genes and providing a specific identity to each cell type. Research on identical twins (monozygous, or MZ, twins) conducted by Fraga and his colleagues at the Spanish National Cancer Center indicates that perhaps identical twins do not remain identical. Their studies reveal that the patterns of epigenetic modifications in MZ twin pairs increasingly diverge as they become older, or if they have led different lifestyles and have spent less of their lives together. The team found that early in life, twins are almost indistinguishable in the manner in which their genes are expressed. Among older sets of twins, however, significant differences in the gene-expression profiles were apparent in 35% of the study group. Study results suggest that the underlining role of environmental factors is significant. The findings also show that the manifestation and frequency of disease onset in the twins are affected by external and/or internal factors which alter epigenetic modifications and genetic information. Diet, physical activity, and other lifestyle practices are external factors that have a long-term influence on epigenetic patterns and modifications. Some human cancers have already been linked with epigenetic changes. Nature and nurture continuously interplay, and epigenetics may be the mechanism between them that explains how the same genotype can be turned on or off in different ways. |
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