A 34-year-old U.S. man was the first-ever recorded case of a human “chimera,” or a person composed of two genetically distinct cells. In this case, the man has extra genes that were thought to be absorbed by his deceased twin while still in the womb.
In June 2014, a couple (who wishes to remain anonymous for their personal privacy and the security of their medical records) had a son with the help of a fertility clinic, but were puzzled when the child had a blood type that didn’t match either of his parents.
When several paternity tests (even from accredited labs) suggested that the man wasn’t actually the father, the couple was stunned–and outraged, thinking the fertility clinic had made some mistake.
It was only when the couple decided to test both the father and son with a direct-to-consumer genetic ancestry test that they got different results, which turned out to be even more confusing.
The results stated that according to the DNA, the son was actually more like the man’s….nephew (genetically speaking, of course). But how could this be?
In essence, the DNA from the father’s unborn twin brother has actually contributed to the DNA of the man’s own son, effectively “fooling” a paternity test. According to one article, “About one-in-eight single childbirths are thought to have started as multiple pregnancies. Cells from these miscarried siblings are sometimes absorbed in the womb by a surviving twin, but are only rarely discovered by surprises such as the paternity test puzzle.”