I’VE recently had a few friends asking me about personal DNA testing. For a small fee, you send some saliva to a genetic testing company, and they’ll sequence your DNA.
Most people, like my friends, are interested in DNA testing to find out about their ancestry. For them, DNA testing is a bit of fun, something to chat about over dinner.
But for some people, DNA testing has been life-changing.
Some people have used genetic testing to find biological parents or other relatives. Because our DNA is inherited, people who are closely related will share some DNA. To find relatives, people upload their DNA sequences to public databases, which can be searched to find close genetic matches.
Recently, another use for public DNA databases has emerged: catching killers.
On May 5, 1986, 18 year-old Janelle Cruz was found in her home, brutally raped and murdered. There were no witnesses, and no immediate suspects. However, the killer left something extremely important at the scene: a DNA sample.
On April 24, 2018, Joseph James DeAngelo, now known as the Golden State Killer, was arrested and charged with Janelle’s murder. And it all came down to that DNA sample. Back in the '80s, DNA profiling was still unknown.
For many years, the DNA sample remained locked away, unused.
But as DNA analysis became a common tool in forensic investigations, police returned to the sample. They looked for matches in their national forensic databases, but found nothing. The killer’s DNA wasn’t in their databases. Then they had a novel idea. Why not compare the DNA sample to the sequences uploaded by the public into the online genetic databases? It was a long shot, but it paid off.
Police didn’t find an exact match, but they did find sequences similar enough to indicate a definite family relationship. This discovery narrowed the pool of suspects down to the members of a single family. From there, it was simple to determine which family member was in the area at the time of the murder. Police collected a DNA sample from DeAngelo, and compared it to the sample collected decades earlier. It was a perfect match.
How many more cold cases might be solved in the same way? Is this a breakthrough in policing, or an ethical can of worms? The debate rages on.
But a quick word of warning – once your genetic data is public, there is no going back.
Dr Mary McMillan is a lecturer at the School of Science and Technology, University of New England
