Who’s DNA is It? By Brian Simpson

     This is pretty interesting: a man’s semen shows the DNA of his bone marrow donor after transplant; talk about genetic colonisation!
  https://interestingengineering.com/mans-semen-only-shows-dna-of-his-donor-after-bone-marrow-transplant?utm_source=Facebook&utm_medium=Article&utm_campaign=organic&utm_content=Dec10
  https://www.nytimes.com/2019/12/07/us/dna-bone-marrow-transplant-crime-lab.html

“Three months after his bone marrow transplant, Chris Long of Reno, Nev., learned that the DNA in his blood had changed. It had all been replaced by the DNA of his donor, a German man he had exchanged just a handful of messages with. He’d been encouraged to test his blood by a colleague at the Sheriff’s Office, where he worked. She had an inkling this might happen. It’s the goal of the procedure, after all: Weak blood is replaced by healthy blood, and with it, the DNA it contains. But four years after his lifesaving procedure, it was not only Mr. Long’s blood that was affected. Swabs of his lips and cheeks contained his DNA — but also that of his donor. Even more surprising to Mr. Long and other colleagues at the crime lab, all of the DNA in his semen belonged to his donor. “I thought that it was pretty incredible that I can disappear and someone else can appear,” he said. Mr. Long had become a chimera, the technical term for the rare person with two sets of DNA. The word takes its name from a fire-breathing creature in Greek mythology composed of lion, goat and serpent parts. Doctors and forensic scientists have long known that certain medical procedures turn people into chimeras, but where exactly a donor’s DNA shows up — beyond blood — has rarely been studied with criminal applications in mind. Tens of thousands of people get bone marrow transplants every year, for blood cancers and other blood diseases including leukemia, lymphoma and sickle cell anemia. Though it’s unlikely that any of them would end up as the perpetrator or victim of a crime, the idea that they could intrigued Mr. Long’s colleagues at the Washoe County Sheriff’s Department, who have been using their (totally innocent) colleague in IT as a bit of a human guinea pig.”

     Well blow me over. It raises a few problems for DNA forensics, which has become something of a religious cult, supposedly yielding astronomical probabilities for identification cases, which would be wrong in these cases of genetic chimeras.