[fxm4139]

Yes, my brother had a stem cell transplant using my stem cells. At one point a year after transplant he got some graft-vs-host disease and one of the first tests they do is a Chimerism test to see how much percent of his blood stem cells are actually mine. The way they do that is by comparing his blood to a base sample of mine. Or otherwise, they could compare his blood to his hair sample (which retains his old DNA), and see if its different. I'm obviously over simplifiying it, but as far as the crime situation some others are talking about on this thread, note that the identical footprint will only be in the DNA in blood. If you take skin/hair etc, it will still have the original DNA set.