Are You a Chimera?
"Chimera" is pronounced ki-meer-uh.
What is a chimera? In biology a chimera is a lifeform with two DNA profiles. For example, a human chimera's hair sample might not match their saliva sample. It's crazy but true!
The word "chimera" comes from ancient mythology. It refers to an imaginary creature comprised of various animal parts, e.g., a lioness combined with a snake and a goat. Scientists didn't realize until very recently that people and other animals, along with plants, can express more than one set of DNA. In fact, you might be a chimera!
Some people are rather obviously possible chimeras. For instance, if you have mostly coffee-brown skin plus patches of whitish skin, you might be expressing two different sets of DNA. Other human chimeras stand out for having hair that doesn't match the rest in color or texture. Intersexed people may also be chimeras. However, many human chimeras have no external signs of their unusual condition. Their second set of DNA might only operate in their kidneys, for example.
This article about human chimeras was inspired by the Discovery Channel special entitled "I Am My Own Twin."
How Do People Become Chimeras?
Chimeras are created when four parent cells (or two fertilized eggs) become fused. Transplants can also create chimerism since they introduce foreign DNA.
Although human chimeras are likely as old as our species, DNA wasn't identified until 1952 with Rosalind Franklin's X-ray crystallography. A human chimera was announced the following year: In 1953 in the British Medical Journal published the first study of a human chimera. The woman in the study had two distinct blood types. Her chimerism came from her twin brother, who was still alive. She had absorbed some of his DNA while in the womb.
Being a twin seems to be the most common way of becoming a chimera. The other twin might be unknown since twin pregnancies sometimes end up as single births.
Despite the publication from 1953, most medical doctors were unaware of chimerism just a decade ago. The Discovery episode "I Am My Own Twin" documents two cases of chimerism in the US that have helped raise awareness.
"I Am My Own Twin"
In the first case, a Washington woman named Lydia Fairchild applied for welfare assistance. She was required to prove her relationship to her children. Oddly enough, her children's DNA tests suggested that she wasn't their mother. However, it did confirm that their father was their father! Prejudice worked against Fairchild; people figured she'd been caught attempting fraud. She couldn't get legal representation because lawyers regarded DNA "evidence" as irrefutable.
Fortunately, a "more respectable" woman in Boston was experiencing a related situation. Karen Keegan was a 52-year-old teacher. When she needed a kidney transplant, her three sons were tested for DNA compatibility. The tests suggested that she lacked a maternal relationship with two of her three sons.
While Fairchild was fighting off the state prosecutor, Keegan was in a position to pursue the DNA mystery. Her doctor pored over medical journals and networked with colleagues. She then surmised that Keegan was a chimera and began testing.
First, doctors took DNA samples of Keegan's hair and skin. When these samples proved fruitless, they moved on to sample her internal organs. That's when they found a different set of DNA. Genetically, two of her sons appeared to be descendents of her husband and a vanished twin.
Luckily for Fairchild, Keegan's experience was documented in a medical journal. When word reached Washington, Fairchild was finally able to secure legal representation, welfare, and custody of her children.
Implications of Chimerism
As Fairchild's judge observed, chimerism calls into question the validity of DNA tests. Positive matches remain unchallenged but all "negatives" are now suspect. The phenomena of chimerism calls into question many paternity suits and other court cases. In a small percentage of couples, it might also help explain infertility.
Learn More About Chimeras
- Chimeras: Transplants & Failed Paternity Tests
Genetic testing isn't perfect, as revealed by the case of Lydia Fairchild.
- Animal-Human Hybrids Spark Controversy
Mice with human brain cells and humans with pig tissue are only two real-life examples of chimeras. This article from National Geographic explores the ethics of creating human-animal hybrids.
Marc on July 20, 2020:
Does this have anything to do with a person's body being larger or different on the right side vs. The left side?
Peshmerga on April 20, 2019:
Are there any court cases from a chancery, district, appellant or supreme court, either state of federal that you or your readers can give me that has been reported about human chimerism?
Particularly, where a man was excluded as the father of a child with the baccal swab but was later determined the actual father due to his human chimerism that could be proven through sperm analysis. send to firstname.lastname@example.org ..... Thanks
Ian Slayne on June 01, 2015:
"Good question, Alexander! The DNA would be from a twin, the same person who would probably be an ideal organ donor had they actually lived. Also - and this is just my speculation - maybe some births are miscarried because of a rejection after fusion."
During development the fetus is highly protected from the outside world. It is during development that the immune system of the fetus is learning to not attack "self". So during the developmental state it is very easy for the embryo to accept other cells as "self".
MariaVictoria on May 30, 2015:
Chimeras as real and yes they do carry two or more DNAs, that´s one of the reason why so many criminals are still free.
Catherine Giordano from Orlando Florida on February 20, 2015:
This is fascinating. I'm concerned about those negative DNA tests in criminal cases.
SantaCruz (author) from Santa Cruz, CA on January 04, 2015:
Hi, M. There are lots of reasons to be an emotional mess. ;-) Why did your doctor mention chimerism?
The relevant testing would be comparing DNA samples from different systems in your body. As the "I Am My Own Twin" documentary shows, this could take awhile unless you get lucky with the parts you compare.
Sorry, I don't feel helpful but wanted to acknowledge your comment... Best wishes in the new year.
M on January 02, 2015:
This was amazing to read about the bipolar. My doctor just introduced me to the term chimera last year. I'm am and have always been an emotional mess. Is there a way to do other testing anything to get help? I am at my end. THANK YOU.
Laurennicole on September 16, 2014:
I am my own twin, as well. Used to feel very alone. Always felt like I was two people in one, even when I was a young girl. When I was seven, my mom have me the run down. Her first obgyn thought we were an ectopic pregnancy and put us on the schedule to be aborted. My mom, in all of her intuitive skepticism, went for a second opinion from a different doctor. Thankfully, the second doctor denied the ectopic claim. As my mom was rejoicing, the doctor confirms the real truth.. She was carrying twins. We were lucky to not be aborted.
Fetal Reabsorption is the technical name, but the general public seems to know it more as Disappearing Twin Syndrome. At seven, trying to comprehend absorbing my twin was a bit much. It sound like some Wes Craven film, thought I mangled and ate said twin. I was comforted and assured that wasn't how it happened.
A lingering feeling that I have pondered relentlessly since young childhood started to have a formulated answer.. Or base to the answer. I am physically female. Mentally and emotionally, also female.. Mostly. Have always inherently known my twin is a male. This led things to be quite difficult and intense growing up. Slowly, years go by and my arsenal of research has grown. I look forward to someday completely comprehensive DNA testing to confirm that which I already know to be truth.
Not a huge astrology (pseudoscience) fan, but on top of being a chimera, we are of the Gemini variety. I am my own twin and both twins have a very dual way of thinking. Helllllooooo four people?
Androgynous and free spirited. No extra external body parts. Internally, I have so far been informed of two ureters connecting my left kidney to my bladder. One ureter is normally one each side. The two left ureters together make up the size of a single ureter. Thank you kidney stones, however terrible.. Would not have known that until probably much later.
Have read that a lot of chimeras are diagnosed as bipolar. Feel like that is probably a copout. My emotions fluctuate quickly, but rationally and in a linear fashion. What does one expect when you have two souls inhabiting one physical being?
If anyone has any sites or info they can share, would enjoy reading it.
SantaCruz (author) from Santa Cruz, CA on April 25, 2013:
Thank you, Vanderleelie :-). It always leaves me wondering whether I'm a chimera too...
Vanderleelie on April 24, 2013:
Very good hub - well researched and written. I find it fascinating that the Greeks incorporated aspects of this condition in their mythology and imagery centuries ago. Voted up and interesting.
SantaCruz (author) from Santa Cruz, CA on October 05, 2012:
Wow, Lou! It sounds like that's right. The "miscarriage" may have been a miscarriage of a missing twin, but not completely, if he or she became part of your daughter. I imagine this story would be kind of shocking for you! Our bodies are amazing...
Lou on October 05, 2012:
My 3 year old has green eyes, however her right eye (iris) has a brown stripe. She also has brown hair, and has a large section of red hair. She also has a patch of skin that is different. Early in my pregnancy, the hormone levels were really high, and started to drop off, the doc. told me that he thought I was having a miscarriage. However...I did not. Perhaps she is a chimera
nick on June 29, 2012:
They do not reject the organs and parts probably because they're immune system formed when their body already had mixed parts so it recognizes all of it as belonging there and doesn't attack it. Put b blood into an a type they reject it but ab which actually means they have both a & b blood has no problem.
SantaCruz (author) from Santa Cruz, CA on January 31, 2012:
Good question, Alexander! The DNA would be from a twin, the same person who would probably be an ideal organ donor had they actually lived. Also - and this is just my speculation - maybe some births are miscarried because of a rejection after fusion.
Women retain part of their children's DNA for many years, sometimes for decades after childbirth. The fetus's cells actually have beneficial effects, something like how stem cells can adapt to a new host and make repairs. There's real research published about that :).
Alexander Silvius from Portland, Oregon on January 31, 2012:
Very interesting, but I admit I have a very hard time swallowing this one. If organ transplants require special medicine to stop rejection, then how can a whole different DNA be accepted by your body?
Simone Haruko Smith from San Francisco on January 04, 2012:
I had no idea that such a condition even exists. So fascinating!
Larry Fields from Northern California on January 03, 2012:
Wow! Voted up and interesting.
I'd never heard of human chimeras of the type you describe. However there is precedent. It's said that a tiny fraction of human DNA, and of pig DNA, was originally contributed by viruses. The viral DNA integrated itself with the host DNA, including some eggs or some sperm. Obviously, the beasties did not kill their hosts, and may have inadvertently conferred small genetic survival advantages.
Anyway, the original 'infected' hosts could be thought of as chimeras. However that type of chimera-ism is not nearly as dramatic as the mixed eye color photo in your hub.
SantaCruz (author) from Santa Cruz, CA on January 02, 2012:
KJ, I had the same thought! This area of research is very new. Supposedly though, men with twin sisters are more than twice as likely to be homosexual as those without twin sisters. Is this because they swapped DNA or because of social factors? For example, is a gay man with a twin sister more likely than a gay men without a twin sister to accept himself and identify as gay?
Also, older women are supposedly more likely to have gay sons. (I need to get stats to back this up.) This could go back to cell division or have social influences too.
kjforce from Florida on January 02, 2012:
Could this also be a possibile link between transgender and homosexuality ? I have never read any studies regarding the correlation between the two...any knowledge of ?
Kimberly Schimmel from North Carolina, USA on January 02, 2012:
Fascinating!I certainly learned something new.
Ed Michaels from Texas, USA on January 01, 2012:
Very interesting. Thank you for the info.