system
Given the following post, respond as if you're commenting on Reddit:
human
Does the tissue from a transplant retain the DNA of the donor or change to that of the host?

I was thinking about this the other day and my girlfriend and I were arguing about it. When, for example an organ such as a heart or a kidney is transplanted into a host, will a biopsy of the cells after some time show cells with the host's DNA or the donor's DNA?

Related, are the cells that replace the cells in the organ after apoptosis over time made from the host's own cells or from simple mitosis of the donor's cells?
gpt
There are some exceptions of tiny fractions of cells, but by and large, the organs remain the donor's DNA.  There's some evidence that recipient cells can (at very low frequencies) also contribute to the new organ.  Renewal of the organ typically comes from the donor cells, not from the recipient.  That's why patients have to remain on anti-rejection drugs for the rest of their lives.

One major exception to this is bone grafts.  Those are typically just killed donor bone, which provides a matrix for host cells to incorporate and use as the substrate for new bone.