The invention that allowed for the advancement of genetic research in the 20th century is the polymerase chain reaction (PCR). Developed by Kary Mullis in 1983, PCR revolutionized molecular biology by allowing scientists to amplify specific DNA sequences rapidly and accurately. This technique has facilitated groundbreaking research in various fields, including genetics, forensics, and medical diagnostics. PCR made it possible to analyze tiny amounts of DNA and has led to significant advancements in our understanding of genetic diseases, evolutionary biology, and biotechnology.