Human chimeras are a popular topic for TV shows and crime scene dramas. This extremely rare and interesting genetic condition can lead to the question,“Can my DNA Paternity Test be wrong because I’m a chimera?”
Named for the mythical monster with a lion’s head, a goat’s body and the tail of a snake, human chimeras have two or more genetically distinct types of cells in their bodies. This anomaly is thought to be caused by the absorption, or fusing, of twins before they are born. This would cause the chimera to carry two sets of DNA in their body. One set of their DNA and one that would have been their twin’s DNA. This second set of DNA can show up anywhere in the body. A second, distinct set of DNA may be present in the skin, blood, or even reproductive organs of the chimera. This was what happened in the case of Lynda Fairchild, profiled in the ABC documentary.
She’s her own Twin
Fairchild underwent DNA maternity testing shortly after the birth of her child. Results showed a poor match, as if she was the baby’s grandmother. It was concluded that Fairchild may have been a chimera, her body the result of the fusion of two non identical embryos at the earliest stage of development. Different parts of her body could have come from different cell lines. Further testing indicated that cells taken from her reproductive organs, contained different DNA than those taken from her mouth for the DNA testing and were a match to her children.
Though cases like this are often given a lot of press, their occurrence is very rare. No one knows exactly how many cases of human chimera there are, but most studies cite only 30 reported cases in all of human history.
What does this mean for DNA paternity testing?
An inclusion, or “positive” DNA paternity test shows that an alleged father and the child share the same DNA. Therefore that man is considered to be the biological father. The father’s DNA was passed to the child, and the loci (markers) all match up. It’s virtually impossible (that is, very, very unlikely) that possessing two sets of DNA would make someone appear to be a father when they are not. Matches at all locations indicate a positive paternity test result, even if the father is a chimera.
An exclusion (when a man is not the father of a child) could potentially be affected, by someone being a chimera. It is possible for a chimera to pass one set of DNA on to their child but show a second set of DNA with a cheek swab, as in the Linda Fairchild case. Even so, the child and the father would still likely show a partial match, similar to that of a child and an uncle, since the second set of DNA would be that of the father’s unborn twin.
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carolyn gray says
A paternity dna test was recently done for my son, myself and the alledged father. We had the legal test done. The result came back negative. I do not think the result is right. I know you probably hear this all the time-and I understand that but for good reason I think it is wrong. I have been reading about this and am needing to know is there any chance it could be wrong. Also, would a blood test be better or a waste of money? The alledged father is 62 yrs. old and the son is 29. There are no issues involved with this. We were all 3 hoping the tests came back positive and I was so sure that it would Thanks so much. . Thanks so much.
IDENTIGENE says
Hi, Carolyn. Inasmuch as you had a legal test done, there is no question that the DNA samples tested belonged to the right participants. You didn’t mention if you tested with us or not, and I can’t speak to the processes of other labs, but I can speak to ours. Whenever we get a negative result, a different technician runs the test again, to double-ensure test findings. As a highly-accredited lab, our processes and protocols for handling and testing samples are very strict, so results are 100% accurate. Science doesn’t have opinions or take sides, and unfortunately in your case the results weren’t what you hoped for, but they are what they are. As to your other questions: A blood test is no more accurate than a cheek-swab test…it just hurts! So, as you mentioned, it probably would be a waste of money. For your own peace of mind, you can always test again, but chances are overwhelming that the results will be the same. This sounds like a tough situation and I wish you all the very best.
Mom2Girls says
I recently got a DNA test on my daughter because her father requested it. The results came back as him being excluded as the father but I know 1,000% he’s the father of my daughter because I wasn’t involved with no other man before, during or after I got pregnant. This has me very confused and questioning alot about scientists and DNA test results. My baby and her dad match up with 13 out of 20 locus and the ones that don’t match they’re only 1-4 points off. I am going to get a lawyer to subpoena his mom to do a grandparentage test.
Identigene says
Hi! Did you get a legal test done, or an at-home test? With a legal test, every aspect of testing, from collections to submission of DNA samples, is supervised by a witness. This ensures that the possible father or mother doesn’t submit someone else’s samples. That’s what I would suggest you do first instead of doing a grandparent test. A straight paternity test is always the preferred choice. This science is sound and all courts accept it as such, which is why they all use DNA testing to establish paternity. There are processes in place to prevent human error during testing. If an accredited lab is used, then you can be sure the results are correct for the samples the lab is provided.