Chimerism, the presence of two genetically distinct cell lines in an organism, either is acquired through the infusion of allogeneic hematopoietic cells during transplantation1 or transfusion2 or is inherited. In fraternal twins, chimerism occurs by means of blood-vessel anastomoses. A less common cause of congenital chimerism — so-called tetragametic chimerism — occurs through the fertilization of two ova by two spermatozoa, followed by the fusion of the zygotes and the development of an organism with intermingled cell lines.3 Examples have been found in mice4 and other mammalian species,5,6,7 including humans.8.
Not me. Biology is icky and complicated. I always skip the biology ones in Scientific American. I'm only smart enuf to do rocket science!
--Boris