A 34-year-old man has just had the shock of his life. After failing his own son's paternity test, doctors found that the man's son carried not his father's DNA, but his long-dead uncle's. The situation is the first reported case of a paternity test being fooled by a human chimera, a person with extra genes that were absorbed from a twin who was lost in early pregnancy, reports the Independent.

It all started when an American couple, whose child was conceived and born through the help of a fertility clinic, found that their otherwise very healthy child did not have the same blood type as either of his parents. This concerned the baby's father, who took a paternity test and discovered that his DNA did not match that of his son's.

The couple was initially upset, thinking that there must have been a mix-up with the sperm used by the fertility clinic. However, the clinic assured them no mix-ups occurred, reports Fox News.

The couple eventually got help from Stanford University geneticist Barry Starr, who advised the father to take a DNA ancestry test instead. Sure enough, the results of the test showed that the child carried the genes of his uncle, making his dad a "human chimera."

Further tests revealed that the father's body exhibited more signs of human chimerism, including different tones in his skin and DNA variations in his semen.

As remarkable as the case is, human chimeras are actually not that rare, as approximately one in every eight childbirths are thought to start as multiple pregnancies. In these cases, there is a substantial probability that cells from miscarried siblings would be assimilated in the womb by the surviving twin.

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