touch+go DNA

Here is a description of "touch DNA" from Scientific American:

Here’s how it works: Investigators recover cells from the scene, then use a process called polymerase chain reaction (PCR) to make lots of copies of the genes. Next, scientists mix in fluorescent compounds that attach themselves to 13 specific locations on the DNA and give a highly specific genetic portrait of that person. The whole process takes a few days, and forensic labs are often backed up analyzing data from other cases.


These 13 locations were carefully chosen because they are highly variable between people and do not give away any specific information, such as race, gender, personal health or genetic disease. The reason: authorities don’t want personal health information being used for law-enforcement purposes, such as interrogations. The chance of DNA profiles from two different people having the same genetic signature is vanishingly small.


The trick to finding these cells: context. If clothing is removed from the victim, as it was in the Ramsey case, a forensic specialist could try to guess where it might have been handled—perhaps the waistband of a pair of pants—and swab those areas with a Q-tip or a blade. But in cases like the JonBenet Ramsey murder, which has tripped up authorities for over a decade, it can provide information that leads to a killer—or at least exonerates the innocent.

It's not clear what type of variation they are using, but I could imagine microsatellites. There are several confusing aspects of this description. If the 13 loci are specific to an indiivdual, common sense dictates it a person of the same ethnicity will be more similar than from another ethnicity. Genetic variation does indeed indicate ethnicity, even if you only have 13 loci. Also, we know from anthropological genetics that there is a massive amount of DNA everywhere, that is pretty amazing with as little as 16 chromosomes (8 cells) you can get individual profiles.