Thomas Shaddack wrote: > 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?
Nope. Already they have DNA from all over in the sample. Bacteria if nothing else. Probably other humans. So if something from you matches something there, you are spotted. If you were trying it on you would do best to spray around DNA from a close relative so they can't tell the difference. Think - you are a suspect. They find 2 human DNA signals at the scene of the crime, one from you, one from someone quite different from you. Well, they can look for the other guy in their own time, but they've got you. If they are using a stringent enough test (often they don't) the odds against it not being you are huge. But if they have 2 almost-but-not-quite different sequences - well, how can they be sure tht the one that looks like yours isn't really the other one amplified badly (which happens)? NB - the vast majority of forensic DNA evidence is used to support the defence.
