Epigenetics which governs whether specific genes in the body are turned on or not, has broad effects on health and development, ranging from the propensity to develop cancer to a disposition to become fat or thin. That has made epigenetic inheritance—the idea that these patterns of gene expression can be passed from parents to children, grandchildren, and beyond, the subject of profuse research. Some investigators have begun to treat it as settled science.
But has science proven that these are transgenerational effects? Far from it, said Karin Michels [adjunct professor of epidemiology at Havard School of Public Health] First, she pointed out, evolution militates against epigenetic inheritance. Epigenetic changes take place through three different mechanisms, the best studied of which is DNA methylation. Methyl groups, a methane-derived group of atoms that are layered on top of DNA molecules, provide instructions for which genes should be turned on or off—but during reproduction, mammalian cells go through two full cycles of demethylation. That process strips all methyl groups, and thus epigenetic information, from germ and embryonic cells. To date, there is no evidence that epigenetic information can survive two rounds of this biochemical cleansing.
Michels emphasized that epigenetic inheritance may exist—but it has not been proven. And given the current epidemic of sedentary behaviors and obesity, she concluded, perhaps the mechanisms that strip our reproductive cells of the memory of such epigenetically modulated states from one generation to the next are “a good thing!”
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