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Stranger than Fiction In extremely rare cases of vanishing twin syndrome, two early stage embryos fuse into a single embryo containing two unique sets of DNA. The surviving twin becomes what's known as a chimera, essentially two people in one body. Chimeras can have different sets of DNA in different body parts. For instance a male chimera can have one type of DNA in his skin cells but what appears to be an entirely different person's DNA in his sperm cells.
A 2003 study in the New England Journal of Medicine by Dr Margot Kruskall of the Beth Israel Deaconess Medical Center in Boston, Massachusetts, reported the case of a mother who required a kidney transplant. All three of her natural sons were tested as potential donors, but only one appeared to be her biological son, although she gave birth to all of them. Genetic tests revealed that the patient was a chimera, a physical blend of fraternal twin sisters and her ovaries produced eggs belonging to both twins, thus she could give birth to three sons who were genetic half-brothers; one of them sharing DNA with his mother and two sons sharing DNA with their vanished aunt.
According to the November 2003 New Scientist magazine. Some chimeras do have unusual physical features. For example, one girl was discovered to be a chimera because her eyes were different colors, one brown, the other hazel. Others have come to light when doctors investigated problems with their reproductive systems, and found that they had structures from both male and female reproductive organs as a result of having cells of both sexes in their bodies. But most probably go through life utterly unaware of their unusual constitution.