Single nucleotide polymorphism (SNP) typing was a method of DNA analysis and comparison whereby selected segments of a genetic genome were examined, and used to determine matches to other DNA samples. This was the method most commonly used by Starfleet and other agencies in the 24th century, as fuller analyses of a DNA sample were too cumbersome, and raised individual privacy issues.
Federation deep-cover intelligence agents had their DNA selectively manipulated to pass such SNP typing tests. During the investigation into Dr. Jennifer Almieri's death in 2377, it was determined that the individual presenting himself as Dr. Preston Strong likewise had his cellular DNA altered in such a way to pass a SNP typing test. (CoE eBook: Ghost)