Does a bone marrow transplant make a good alibi?

Heymatt:

I am male, over 50 years old. I know who my parents, grandparents, and great-grandparents were. That's easy. What I don't know is whether any of the actual cells, molecules, or tiny atoms of their bodies still exist in my own body?

-- Inheriting in I.B.

Matt:

If I were to commit a crime and accidentally leave DNA evidence, could I then have a bone marrow transplant to change my DNA so as not to get caught?

-- Lori, the net

Don't quit your day job, Lori. As an escape plan, this one is not foolproof. But UCSD geneticist Ethan Bier congratulates you on your devious turn of mind. The transplant would change only your blood cells, and there's no guarantee it would change all of them. You could end up with cells from both sources, depending on the dominance factor in the transplanted marrow. (In which case, your best defense might be split personality.) If the DNA evidence was hair, though, looks like you'd need a hair transplant too-- at the Hair Club for Felons?

So if we can't reliably pin the crime on the marrow donor, can we use molecular biology to finger granny? Naw. The truth is, you don't even have many of the same molecules you had during your own personal babyhood, since cells are continually replacing themselves. Any common material would have long since been lost. You're a whole new you. And if you take a good look at the family album, would you really want granny's actual nose anyway?