As organisms interact with their environment, genes can be turned down, or switched off, through a process called methylation. When a gene is methylated, a chemical group gloms on to parts of it in the same way a bodyguard runs paparazzi interference by sticking close to a celebrity leaving a Hollywood nightclub. This can make the gene’s on-off switch, its promoter, less accessible to the RNA polymerase enzyme that copies the gene’s instructions for making a protein. The gene is there, but it’s been turned off, or down. The study of this phenomenon is called epigenetics. In addition to a
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