I'm fascinated by chimeras -- organisms made up of cells of varying genetic composition. It happens naturally in humans with odd implications. In one case, initial tests on a woman's son, who was naturally conceived and delivered, indicated he was not genetically her offspring. In fact, the mother was a chimera, and the ovary/egg cells which had contributed to her son were of a different genetic makeup from her blood cells, used for other profiling.
Dr. Ann Reed, chairwoman of rheumatology research at the Mayo Clinic, who uses sensitive DNA tests to look for chimerism, finds that about 50 to 70 percent of healthy people are chimeras. The more scientists look for chimerism, the more they find it. It seemed not to exist in the past, she said, because no one was explicitly looking for small amounts of foreign cells in people's bodies.
"Some believe that if you look hard enough you can find chimerism in anybody," said Dr. Reed, who also has not been involved in the Hamilton case. It is so common that she thinks there must be a biological reason for it. It also may cause problems, she and others say.