Three months after his bone marrow transplant, Chris Long of Reno, Nevada (USA), 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 It had all been replaced by the DNA of his donor, a German man he had exchanged just a handful of messages with. However, four years after his lifesaving procedure, it was not only Long’s blood that was affected. Swabs of his lips and cheeks contained his DNA – but also that of his donor. Even more surprisingly, all of the DNA in his semen belonged to his donor.
