Watching local TV, a police brass with three stars is talking about DNA evidence.
Losing samples of DNA is quite inavoidable; hair falls out, skin peels, all you need to get for positive identification is one single cell. After collecting the sample, you amplify it (create much more DNA molecules) using PCR (polymerase chain reaction), making lots of copies of the DNA molecules in the sample. Then you take the mixture, split the huge molecules to smaller fragments using enzymes (I hope I remember it well), and then separate the fragments using eg. electrophoresis. Then you spray the gel strips with something that binds to the DNA fragments, light it with UV lamp (which causes the DNA stripes to shine), and get a photograph that resembles bar code. Then you compare the bar code with the reference samples. This is the old approach used typically for tests in eg. paternity lawsuits. I suppose there are newer, more modern, faster automated methods, but the principle should be the same. But now how to avoid leaving random DNA traces? What about giving up on NOT leaving traces and rather just use eg. a spray with hydrolyzed DNA from multiple people, preferably with different racial origin, thus still leaving fragments like hair or skin cells, but contaminated with wild mix of DNA, so the PCR-copied mixture will be unusable for reliable identification? In the future, when gene therapies will be well-mastered and common, it should be possible to introduce entire new genes into the skin cells themselves; if they will not penetrate too deep into the skin, the modified cells will grow away later in time. The viral vector could be administered as eg. a spray or a bath. (Using deeper-penetrating techniques it should be possible to do things like permanently change skin color, eg. by disabling or stimulating melanine production, or even achieve a chameleon-like effect. Or selectively applying the change using a method similar to tattoo, just using a retrovirus vector instead of ink. Genetics WILL be used in cosmetics once the technology will become safe/cheap enough.) Just musing, and curious if/where I have errors in my ideas...
