[ WP ] Scientists are conducting human experiments in which non-expressed genes are artificially turned on

[ OT Realistic Answer ] 
 
 The idea that we have silent genes is an old school misconception, like the notion that we only use 10 % of our brains. Some genes are not constituitively expressed, and some do not code for protein, but they are transcribed and all play some function at some point ( LNCRNA, miRNA, rRNA, etc ). The only exception is transposons and viral DNA which is integrated into our genome, but even these detrimental genes can be turned on ( apparently ) randomly. There is no mysterious 5000. 
 
 But lets say you do turn on genes that are silenced in certain cell types. Some of these would be globin genes, which would change the way your body absorbs oxygen, may be detrimental to your health. The expression of other genes would cause cells to change to different cell types, or most likely, would result in cell death. We are finely tuned machines, turning on any of these silenced factors would screw up your body's chemistry pretty badly, and might also result in cancer or other diseases. 
 
 Source: IAMA biochemistry PhD candidate.
