Why can DNA testing use very small tissue samples?

DNA testing can utilize very small tissue samples primarily due to a technique called polymerase chain reaction (PCR).1

PCR acts as a molecular copying machine that allows scientists to take a minute amount of genetic material—even as little as a single DNA molecule—and generate billions of copies of a specific segment within a few hours. By repeatedly cycling through heating and cooling phases, the process uses enzymes to synthesize new, complementary strands of DNA, effectively amplifying the sample to a quantity sufficient for detailed analysis.12

This capability is transformative for genetic testing and forensic science, as it enables researchers to obtain reliable results from limited or partially degraded biological evidence, such as a single hair or a small drop of blood. Because PCR does not require the time-consuming process of cell culture, it provides results much faster than traditional methods, facilitating the detection of gene mutations, inherited disorders, and unique genetic profiles.123