There are many ways you can have multiple sets of DNA in your body. When you get a blood transfusion, DNA from the donor can hang out for a week or more. Some people, known as chimeras, are born with two sets of DNA, and others, called mosaics, develop tiny changes in their DNA later in life. But recipients of bone-marrow transplants get a completely new set of DNA added to the one they were born with, and it stays with them for life. Bone marrow is responsible for producing blood cells, so if you have someone else's bone marrow in your body, those blood cells will be made with that person's DNA. That means that a blood test will usually bring back a different DNA result than a cheek swab. And even that is not always the case: one study found mixed DNA in 74% of the cheek swabs of bone-marrow recipients. While this isn't medically harmful to the transplant recipient, it does pose a criminal justice issue. In one instance, a DNA test during a sexual assault investigation matched to a man who was currently serving time in jail, and couldn't have possibly committed the crime. It turns out that his brother, who had donated DNA to the incarcerated man, was the guilty party. We've collected some awesome videos on this topic. Watch them now to learn more.